COLLAP SIBLE CLUTCHING DIFFERENTIAL CROSS-REFERENCE TO RELATED APPLICATION The present application claims the benefit of U.S. Provisional Patent Application Serial No. 6l/727,990, filed November lg,z}lz,which application is hereby incorporated by reference in its entirety' BACKGROUND 1. Field Teachings The present teachings relate to, generally, a clutching differential and, more particularly, such a differential that is collapsible upon itself during installation thereof into a corresponding housing. 2. DescriPtion o-f the Related Art A locking differential of the type contemplated by the present teachings is employed as a part of a drive train of a vehicle to control torque and generally includes a pair of clutch members supported in a housing (or casing). A pair of side gears is splined for rotation to corresponding axle half-shafts. A clutch mechanism is interposed between the clutch members and side gears. A cross-pin is operatively mounted for rotation with the housing and received in a pair of opposed grooves formed on inwardly facing surfaces of the clutch members. In an event requiring differential rotation between the axle half-shafts, such as comering, the higher-speed axle half-shaft advances its clutch to an over-running condition, decoupling it from the torque. If driving terrain provides insufficient traction to activate the over-running condition of the differential or while driving in a straight line, the torque is applied equally to both axle half-shafts' A clutching (or locking) type of the differential is generally employed in a lbur-wheel-drive vehicle or the like, thereby permitting rugged off-road operation of the vehicle. This type of differential is well-known in the aftermarket as a retrofit unit. More specifically, the differential can be retrofitted into an existing conventional housing, such as an original-equipment housing, of the drive train' The housing for a differential can be "one-piece" or "two-piece'" For instance, since the height (dimension that is defined along the rotational axis and can be described also as the..length" or "width") of the differential can be substantial, most originalequipment housings are two-piebe to allow the differential to be assembled/installed in or l5 20 25 l0 inserted into a hrst piece of a particular housing before the second piece of the housing is reunited with the first piece to, thereby, enclose the differential. Typically, however' an ,,open" type of the differential is designed to be employed with one-piece housings' unfortunately, the height of the retrofit of the gearless clutching differentials of the type commonly known in the related art are often too great for the unit to be assembled/installed into the one-piece housings. SUMMARY One aspect of the present disclosure relates to a clutching differential that is adapted to be assembled/installed or inserted into a one-piece housing' In certain examples' clutching differentials in accordance with the principles of the present disclosure are adapted for use in retro-fit applications for installation in existing original-equipment differential housings that have already been installed in a vehicle. This allows exiting differentials such as open differentials to be upgraded to locking differentials. In other examples, clutching differentials in accordance with the principles of the present disclosure can be used in first-fit applications (i.e., installed as original equipment) and may be used in one-piece or multiple piece differential housings. Another aspect of the present disclosure relates to a clutching differential that is collapsible in an axial direction (i.e., along the axis of rotation of the difterential) to facilitate loading the differential into a housing such as a one piece differential housing' In certain examples, the differential is movable in an axial orientation between an extended state apd a collapsed state. In certain examples, the differential can be easily loaded into a ' differential housing while in the collapsed state, and then is axially expanded to the extended state once loaded in the differential housing. In certain examples, the clutching differential has side hubs (i.e., side gears) that axially overlap one another when the differential is in the collapsed configuration. In certain examples, the side hubs can have castellated portions that axially overlap one another when the differential is in the collapsed state. In certain examples. the differential includes clutch mechanisms that are actuated by clutch members to cause torque to be transferred between the clutch members and the side hubs' In certain examples, the differential includes a cross-shaft that rotates with the differential housing and that fits between the clutch members. In certain examples, the cross-shaft is inserted into a groove defined between the clutch members. In certain examples, the cross-shaft is positioned between the castellated ends of the side gears. 15 20 25 2 30 ,^ t0 15 20 . Another example of the present disclosure relates to a differential that allows for reduction of the height of the differential when it is assembled/installed or inserted into the housing. The present teachings further include a collapsible clutching differential for use in a drive train of a vehicle to control torque. The drive train includes at least one rotating member defining an axis of rotation of the rotating member; a housing operatively supported in driven relationship with respect to a remainder of the drive train, adapted to rotate about the axis, and defining a cavity of the housing into which the rotating member extends; and at least one cross-pin mounted for rotation with the housing' The differential includes a pair of side gears disposed in the cavity of the housing, supported for rotation about the axis relative to the housing, and having a torque-transmitting connection to the rotating member. The side gears are adapted to be spaced from each other and collapse uPon themselves such that the differential collapses upon itself. In this way, the collapsible clutching differential of the present teachings is adapted to be assembled/installed or insertpd into a one-piece housing' This is because it allows for reduction of the height of the differential when it is assembled/installed or inserted into the housing. This feature is facilitated by the fact that the internal components of the collapsible clutching differential of the present teachings do not include bevel gears' To this end and in one aspect of the present teachings, the present teachings include castellated gears that are disposed on respective sides of the differential and allow for reduction of the height of the internal components when it is assembled/installed or inserted into the housing. This feature of the present teachings makes it panicularly adapted to be marketed as a retrofit unit, but is also applicable to first-fit applications' RRIEF DESCRIPTION OF THE DRAWINGS Other aspects of the present teachings are readily appreciated as the same becomes more understood while the subsequent detailed description of at least one aspect of the differential is read taken in conjunction with the accompanying drawing thereof wherein: FIG. 1 is a cross-sectional side view of a collapsible locking differential of the present teachings illustrating a drive shaft, pinion gear and ring gear of a drive train; FIG. 2 is an exploded perspective view of the collapsible clutching differential of FIG. 1; 25 30 10 . FIG. 3 is a sectional side view of the aspect of the collapsible clutching differentiar of the present teachings shown in FIG. 2 ilrustrating the differential disposed in a "collapsed" *"lro. 4 is a sectional side view of the aspect of the collapsible clutching differential of the present teachings shown in FIG. 2 illustrating the differential disposed in a "collapsing" state (i.e., a partially collapsed state); FIG. 5 is a sectional side view of the aspect of the collapsible clutching differential of the present teachings shown in FIG. 2 ilrustrating the differential disposed in ano.inserted/installed" state (i.e., an axially extended state); and FIG. 6 illustrates an example one-piece differential housing suitable for receiving the collapsible differential of FIG' 2' DETAILED DESCRIPTION onerepresentativeexampleofacollapsibteclutchingdifferentialofthetype contemplated by the present teachings is generally indicated at l0 throughout the figures' where rike numerals are used to designate rike structure. The differential 10 is designed to be employedasapartofadrivetrainforanysuitablevehiclehavingapowerplantthatisused to provide motive force to the vehicle-for example, an automotive vehicle' More specifically, the differential 10 is desigred to be employed as an aftermarket clutching differential retrofiffed into a one-piece housing of a four-wheel-drive vehicle or the like' Figurelillustratesanaxleassemblyincorporatingthedifferentiall0.The axle assembty is part of a drive train used to transfer torque from a prime mover 15 (eig'' an engine, a motor, or like power source) to left and right wheels 17 ' lg' The differential 10 includes a differential housing 12 (i.e., a differential case) and a differential mechanism 38 (i.e., a differential torque transfer arrangement) positioned within the differential housing 12' The differential housin g 12 carries a gear 14 (e.g., a ring gear) that intermeshes with a drive gearl6drivenbyadriveshaftl8ofthedrivetrain.Thedifferentialmechanism38is configured to transfer torque from the differential housing 12 to left and right half axle half shafts 30,32(i.e., rotating members) that respectively correspond to the left and right wheels |T,lg.Thedifferentiall0isenclosedwithinanaxlehousing2|thatprotectsthedifferential 10 and contains Iubricant (e'g', oil) for lubricating moving parts within the axle housing 21' The differential housing 12 is mounted to rotate relative to the axle housing 21 about an axis of rotation A. [n one example, bearings can be provided between the differential housing 12 and the axle housing 21 to allou,the differential housing 12 to freely rotate about the axis of 15 20 25 30 l0 rotation A relative to the axle housing2l. The left and right axle half shafts 30,32 are coaxially aligned along the axis of rotation A. In certain examples, the axle assembly can be incorporated into a vehicle such as an all-terrain vehicle, a light utility vehicle, or other type of vehicle. The differential 10 of the axle assembly is configured to prevent individual wheel spin and to provide enhanced traction performance on a variety of surfaces such as mud, wet pavement, loose dirt and ice' ln use, torque for rotating the differential housing 12 about the axis of rotation A is provided by the drive gear 16 that intermeshes with the ring gear 14 carried by the differential housing 12. The differential mechanism 38 includes left and right clutches (e.g., disc style clutches) configured to transfer torque from the rotating differential housing 12 to the left and right axle half shafts 30, 32 thereby driving rotation of the left and right wheels 17, l9- When the vehicle is driven straight, the left and right clutches are both actuated such that torque from the differential housing 12 is transferred equally to the left and right axle shafts 30,32. When the vehicle turns right, the left clutch is de-actuated while the right clutch remains actuated' In this state, the differential mechanism 38 continues to drive rotation of the right axle shaft 32 while the left axle shaft 30 is allowed to free wheel at a higher rate of rotation than the right axle shaft 32. When the vehicle makes a left turn, the right clutch is de-actuated while the left clutch remains actuated. In this state, the differential mechanism 38 continues to