.14 HARLEY N. GOULD 



before the beginning of female differentiation, mitotic figures 

 like those shown in figures 8 to 12 may be found in the germinal 

 layer of the gonad, and only in the germinal layer. The direc- 

 tion of division may be parallel to the wall of the gonad, or 

 somewhat oblique-to it ; in any case the daughter products always 

 lie close to the connective tissue sheath ; they are never found in 

 the lumen. The chromosomes are comparatively large and very 

 distinct. The only period of the sexual cycle when these mi- 

 toses have been observed in large numbers is the transitional 

 stage which precedes the assumption of the female condition. 



Contrasted with the dividing cells shown in figures 8 to 12 are 

 those of figures 15 to 20. The difference in size is striking. The 

 character of the metaphase figure is a distinguishing mark also; 

 for in the larger mitoses (fig. 9) the metaphase plate is fiat and 

 the chromosomes are somewhat separated from one another, 

 while in the smaller (fig. 16) it is sheaf-like and the chromosomes 

 are densely packed together so that their individual forms can- 

 not be traced, except in cells which the microtome knife has cut 

 in two. These figures are found in great abundance during the 

 period of spermatogonial multiplication and all through the 

 male phase as long as the testis continues to produce spermato- 

 zoa. They represent the method of division of the primordial 

 male cells and spermatogonia. 



It has been said that in Crepidula convexa (as well as C. for- 

 nicata) there is an overlapping of the male upon the female 

 phase. Perhaps it would be better to say that in these species 

 the egg cells develop relatively early, attaining the condition of 

 the resting oocyte while the male period is still at its height. The 

 writer was interested to know whether there is any cell in these 

 species comparable to the primordial egg cell of C. plana. Fig- 

 ure 5 shows a section through part of the gonad of a minute C. 

 convexa, less than 1 mm. long, and probably only a few weeks 

 after hatching. As the figure shows, there are cells in the germ- 

 inal layer which resemble the primordial egg cells of C. plana, 

 although they are smaller, relative to the spermatogonial cells 

 in the lumen, than the type A cells of C. plana. Actually, all 

 the germ cells of C. convexa are larger than those of the former 

 species. 



