34 HARLEY N. GOULD 



division was at its height. Figure 51 is drawn from such 

 material. 



It is not intended to make a detailed report in this paper of 

 the changes in the young oocytes leading up to the resting con- 

 dition. An account of these processes is reserved for a later 

 publication. Female development of the gonad will therefore be 

 followed only bsiefly. 



The various appearances of oogonial mitosis have already been 

 summarized in figures 7 to 13. The last four of these figures were 

 all taken from the same preparation as figure 51. The double 

 chromatic bodies of the resting nucleus grow more distinct in 

 preparation for division and elongate, forming the prophase 

 chromosomes. It has not yet been made certain whether each 

 chromatic body is concerned in the formation of a single chro- 

 mosome, but probably this is not the case, for the chromatic 

 bodies of the resting nucleus appear to be much more numerous 

 than the prophase chromosomes. In contrast to the chromatic 

 structures in the resting nucleus, which are duplex, the prophase 

 and metaphase chromosomes appear, so far as they have been 

 investigated, to be single; yet when the daughter elements sepa- 

 rate in the anaphase they are sometimes double (fig. 10). 



A certain phase of recent work deserves brief comment here. 

 Kleinensteuber ('13) and Giese ('15) assume a very simple proc- 

 ess of oogenesis in the Calj^ptraeidae which they have investi- 

 gated, including Crepidula unguiformis. Giese's figures purport 

 to show a direct transformation of epithelial cells into growing 

 oocytes. In the three American species of Crepidula the present 

 writer finds a complicated series of nuclear changes preceding 

 the growth period of oocytes. Such a series has also been found 

 in other Gastropods (Paludina, Popoff, '07; Helix, Demoll, '13). 

 The question arises whether the material used by Giese and 

 Kleinensteuber may not have been fixed at a time when the 

 nuclear changes in the oocytes were already completed. 



In figure 51, not only are the oogonial divisions going on, but 

 the nuclear changes in the oocytes are under way. Synizesis is 

 very com.mon in this specimen. It will be observed that there 

 are now no cells free in the lumen, which is indeed very small. 



