I would generate a single catalog entry for the object, (e.g., 2012.123.1 but would identify the separable parts individually as items “a” through whatever, so that the full catalog “number” would be something like 2012.123.1a-k.
Unless I had time to spare, I don’t think I’d get into descriptions of the individual parts, although that could be justified in some instances.
To a degree, the decision would depend upon whether the separable parts, if separated, would or would not be recognizable as elements of the “parent” object. For example, few registrars or curators would assign separate letter suffixes to the drawers of a desk or highboy, even though they are “separable parts,” because (a) they’re unlikely to be separated from their “parent” object in the normal course of their museum storage or exhibition, and (b) if temporarily separated (e.g. for conservation treatment, or for a display that might focus upon details of drawer construction) there is little or no likelihood that there would be any difficulty in returning them to the proper “parent.”
I haven’t a clue as to what a “hemocytometer” is, or how many separable parts one might contain, or whether those parts would be readily identifiable as component elements of that particular gizmo, so I can’t offer any more object-specific advice.