The determination of sex in animal development. 735 



zoa of Pygaera if (p. 565—566) it may be gathered, that here it is 

 the homologue of the wormlike form of Paludina, which is functional. 



From Meves' interesting finds I am inclined to mention one or 

 two other ideas, which have cropped up in the course of the work. 

 His find in Pygaera^ if I have correctly understood him, seems to sup- 

 port the idea of the functional nature of the wormlike spermatozoon 

 or its equivalent in many or all Crustacea, as well as in some other 

 Arthropods. Even the so well known spermatozoa of Ascaris may be 

 of this variety. 



Probably the instances of two sorts of unlike gametes in male 

 Metazoa are far more numerous than we have hitherto supposed^). 

 Sometimes the one sort may be the functional one in the male, some- 

 times the other: but nothing goes to demonstrate two kinds of 

 functional gametes in the male. 



One may, indeed, safely go further and conclude, that in every 

 spermatogenesis in dioecious forms a second form of spermatozoon 

 — a dimorphism of spermatozoa — will, on investigation, be in evi- 

 dence; or that some reason for its absence, such as degeneration of 

 "giant-spermatogonia or spermatocytes", will present itself. As a 

 matter of fact, twofold spermatozoa are, even on the results of re- 

 searches not made in search of such, very common in various divisions 

 of the animal kingdom. They are now known, and not in isolated 



SON calculated that there were about 70000 ova.) Four additional 

 mitoses of this number of germ-cells would give 1048576. With only 

 twenty mitoses from the primitive germ-cell we reach this enormous 

 number. Probably in the female skate there are from the period of 

 the primary germ-cells to the ripening of the eggs nothing like ten 

 additional mitoses. 



Prom the above calculations it would follow, that in the human 

 female embryo there must be seventeen divisions from the primitive 

 germ-cell to the oocytes, yielding at the most somewhere about 131000 

 of the latter. 



1) Apparently another case of this kind is to be met with in 

 Cicada, as recorded in a memoir by E. V. Wilcox (in: Bull. Mus. 

 comp. Zool., V. 27, No. 1, 1895, p. 7 — 8). Here giant spermatogonia 

 and spermatozoa are described. From his account it seems to be clear, 

 that these are mainly in a condition of degeneration, and that such an 

 atrophy may happen at any stage in the development from the spermato- 

 gonium to the spermatozoon. It would appear doubtful , if any of 

 the lai-ger germ-cells really become perfect spermatozoa, and thus Ci- 

 cada would represent a further step in the "degradation" of the worm- 

 like spermatozoon of Paludina. 



