24 
Mitosis in somatic cells is to be found in the hind end of the ali- 
mentary canal in Daphnias whose ages are from 4 to 6 days. It is inter- 
esting to note that newly hatched and very young Daphnias are not 
favourable objects for the examination of somatic mitosis. The dividing 
cells of the alimentary canal, like those of the gonad, show a well for- 
med spindle apparatus and a centrosome, but the massing together of 
the chromosomes on the equatorial plate makes it difficult to decide 
whether the somatic number is 8 or 10. However, the evidence from 
somatic mitosis confirms the results described above, namely, that the 
male Daphnia posseses the diploid number of chromosomes. 
While this note was still in MS. a Paper on » The Spermatogenesis 
of a Daphnid-Simocephalus vetulus« by Robert Chambers’, published 
in the Biological Bulletin, Vol. 25, came into my hands. Chambers 
describes the degeneration of approximately half the spermatids in this 
species, and suggests that they are the male-producing gametes. As the 
specimens of Simocephalus vetulus in Dr. Agar’s collection were too 
old for a complete study of spermatogenesis, and consequently for a 
study of degeneration, I have, since reading Chambers’ Paper, re- . 
studied all the sections of D. pulex used for this note, and have also made 
many new ones and many stained preparation of dissected gonads for 
the purpose of discovering whether in D. pulex a degeneration of sper- 
matids takes place, such as Chambers found in Simocephalus vetulus. 
In the foregoing note it has already been pointed out that many of 
the spermatocyte II cells of D. pulex contain 5 chromosomes, while 
others again show clear cases of the presence of 4 chromosomes. But, 
as such discrepancies occur also in spermatogonial and somatic cells, 
I do not think that this points to a real dimorphism of spermatozoa. 
I can find no trace of degenerating spermatids (in D. pulex). Hence, 
since my observations on D. pulex do not accord with those of Cham- 
bers for Simocephalus vetulus, the question of the male and female 
producing spermatozoa in Cladocera generally must still be regarded 
as an open one. 
6. Der hammerformige Chaetognathen-Kopf. 
Von Dr. Gerarda Wynhoff, Utrecht. 
(Mit 2 Figuren.) 
eingeg. 12. Juni 1914. 
Während meines Aufenthaltes an der Zoologischen Station in 
Neapel wurde durch einige Sagitten mit abweichendem Kopf in einem 
3 Chambers, R., The Spermatogenesis of a Daphnid Simocephalus vetulus. 
Biol. Bulletin 25. p. 134 — 140. 1913. 
