2 72 CALKINS. [Vol. XI. 



ject the following paper is mainly devoted. The history of the 

 nuclear elements proved less easy to follow and the results are 

 less satisfactory, although they present certain new points of 

 interest. 



The nomenclature adopted is that of LaValette St. George 

 (•78), according to which the three principal stages of the devel- 

 oping cells are designated as (i) "spermatogonia," (2) "sper- 

 matocytes," and (3) "spermatids." It is, however, difficult 

 strictly to apply these terms to the Annelida, for the different 

 stages are not confined here to different zones of the testis. 

 In Lumbricus, for example, the later stages occur in the 

 seminal vesicles, while the testes contain only spermatogonia. 

 Careful study of the vesicles has failed to demonstrate in them 

 any definite arrangement or order comparable to the " Wachs- 

 thumszone" or ^'Reifujigssone'' found in many other forms. 



Relative position, therefore, is not a guide to the distinction 

 between spermatogonia, spermatocytes, and spermatids ; nor 

 can dimensions of cells be utilized as a means of recognition, 

 for the same stages are represented by quite diverse sizes and 

 forms. The progressive development of the cell is, however, 

 indicated by differences in the make-up and in the number of 

 chromosomes as many observers have shown, and here, there- 

 fore, a trustworthy basis of comparison may be found. Accord- 

 ing to recent investigations the presence of Vierergnippen in- 

 dicates the late stages of " spermatocytes of the first order " or 

 cells where there are one half the normal number of chromo- 

 somes and where each chromosome is in four distinct parts. 

 "Spermatocytes of the second order" are recognized both by 

 the half number of chromosomes and by the fact that each 

 chromosome is no longer quadruple but double {Zw'eier- 

 griippen, or double chromosomes). Spermatids are recognized, 

 in their early stages, by the presence of single chromosomes of 

 one half the normal number ; in the late stages by the compact 

 and homogeneous chromatin and by the elongating form. The 

 mature spermatozoon consists of head, middle-piece {Mittcl- 

 sttick), and tail, parts which are represented in the spermato- 

 gonium by nucleus, archoplasm, and a part of the cytoplasm, 

 respectively. 



