202 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
logical value, and no chemical property different from that of the sur- 
rounding protoplasm, we have a right to ask why they are tolerably 
constant in number, position, and relationship to other parts of the 
cell. 
The recent studies of Wheeler, Mead, and Wilson and Matthews upon 
fertilization suggest the need of further inquiry into the function of the 
centrosome, 
Wheeler (95) has found in Myzostoma archoplasm and centrosomes 
in connection with the female pronucleus, but never with the male pro- 
nucleus. This is an interesting observation, but it ought to be confirmed 
by further study, since it is directly opposed to the results of Mead 
(95), who found neither archoplasm nor centrosomes belonging to the 
female pronucleus of Cheetopterus, these structures being introduced 
into the egg by the spermatozoón. On this point Wilson and Matthews 
(95) have reached results in the study of Echinoderms which agree 
with those of Mead. The conclusion reached in both cases is essentially 
the same, and is summarized by Wilson and Matthews (p.,320) in these 
words: “The archoplasm of the first cleavage-amphiaster is developed 
entirely from, or under the influence of, the spermarchoplasm (fsper- 
mocentre’ of Fol), and this is derived not from the apex of the 
spermatozoón, but from its base, undoubtedly from the middle piece 
(Toxopneustes, Arbacia).” 
In the spermatids of Caloptenus I have traced the centrosome until it 
becomes the middle piece, and hope to be able to study the early stages 
of fertilization in the eggs of some insect in the near future. 
My warmest thanks are due to Prof. E. L. Mark for the kind advice 
and assistance which 1 have received from him during this investi- 
gation. 
CAMBRIDGE, April 28, 1895. 
