VH] MITOCHONDRIA, ACROSOME 99 



like that of the Golgi apparatus to be mentioned below, 

 varies in different cases. In A scar is , which has a spermato- 

 zoon with a considerable cell body, the mitochondria are 

 carried over into the egg and there multiply and doubtless 

 provide part of the mitochondrial apparatus of the embryo. 

 In Echinoids, as MEVES has shown, the mitochondrial body 

 is carried into the egg as the "middle-piece," which is 

 recognisable to a late stage of segmentation by appropriate 

 staining as a distinct granule, but takes no apparent part 

 in development; and lastly, if MONTGOMERY is correct, the 

 mature spermatozoon of Peripatus is without mitochondria. 

 All this points to their being functional in spermatogenesis 

 rather than as being bodies transmitted by the spermato- 

 zoon for the needs of the embryo. 



The last element in the spermatozoon of which the origin 

 must be described is the acrosome, about which there has 

 been great divergence of opinion. AccordingtoMoNTGOMERY 

 it arises from a body which a'ppears in the spermatid after 

 the second spermatocyte division, and has been called by 

 various writers the sphere or idiozome. The word sphere, 

 however, has often been used as equivalent to centrosphere, 

 that is, the outer layer of "archoplasm" (BovERi) enclosing 

 the centrosome, and although the "sphere" of the spermatid 

 is described in some cases as developing in close relation 

 with the centrosome, in others there is no such connection, 

 so that the two structures are probably quite distinct. The 

 word "idiozome" introduced by MEVES is therefore more 

 satisfactory, but it is by no means certain that the idiozome 

 of the spermatid is in any way equivalent to the body 

 which MONTGOMERY calls by that name in the spermato- 

 gonia (see p. 98). The idiozome or sphere, then, arises 

 in the spermatid usually, but not necessarily, near the cen- 

 trosome, and therefore usually in a position which would be 



72 



