140 ZOOLOGY 



possibility of the actual material being derived from the nucleolus. 

 The yolk nucleus is in this case albuminous in nature (45). 



Sufficient data have been brought together above to show that 

 there is a growing consensus of opinion that the nucleolus, via its 

 extrusions, may be associated with the formation of the albu- 

 minous yolk. It is evident, of course, that there are many dis- 

 crepancies, but many of these may be due to differences of the 

 subject under investigation. Further work may well lead to a 

 general clearing up of this matter. 



Practically nothing more can be said at present regarding the 

 function of the nucleolus, and it is evidently a field in which 

 investigation will be amply repaid. 



SPERMATOGENESIS, OOGENESIS AND YOLK 



FORMATION 



Spermatogenesis. Most of the important features of sperma- 

 togenesis have been described under the headings of Golgi appa- 

 ratus and mitochondria, but a short account is due to correlate the 

 various structures and to refer to the behaviour of some other 

 cytoplasmic inclusions. 



The mature sperm consists of a head, middle piece and tail. 

 The head is made up of a tip called the acrosome and the con- 

 centrated nucleus. The acrosome is usually considered to have a 

 penetrating function, but Bowen does not agree with this (9). 

 According to him, the shape of the acrosome does not lend support 

 to this theory. For instance, in mammalia it is a round, blunt cap, 

 fitting over the nucleus (Fig. 66. G). Furthermore, he maintains 

 that the acrosome is not always terminal. Quoting Goldsmith's 

 Coleopterous work, he says that there the acrosome is at the side 

 of the nucleus, and parallel witli it. In Lepisma he himself finds 

 the acrosome behind the nucleus (9), which reduces the cutting 

 tool idea to an absurdity. Gatenby, however, has re-examined 

 the spermatogenesis of Lepisma domestica (38), and finds the 

 acrosome in the usual tip position, and thinks that Bowen has 

 mistaken the rather large post-nuclear body for it. On these 

 lines Bowen would have misinterpreted Goldsmith's work. This 

 post-nuclear body lies at the bas^ of the head and joins it on 



