189 
which is confluent with the lining of the tubular cavity, and 
lends support to the suggestion that the envelope is not pro- 
duced in any special way by the ovary or its duct, but origi- 
nates from the same cells as secrete the tubarium. The usual 
size of the free ova is from °4 by ‘33 mm. to "5 by -4 mm. 
As regards the distribution of the sexes, all the polypides of 
specimen 10265 that were examined proved to be females, and 
all those of 18551 were males; but I have satisfied myself by 
careful examination of the polypides of specimens 13203, 18633 

Text-Fic. 5. A. and B,—the two ovaries of one polypide of C. gilchristi ; 
C and D,—the two ovaries of another polypide; E, F, G, H.—testes of differ- 
ent polypides ; J,—ripe spermatozoa. A—H are enlarged 50 diameters; J, 
500 diameters. 
and 18655 that the same branch of the colony may have female 
polypides in some of the cavities and males in the others. The 
colony is thus monoecious. Why the specimens 10265 and 
18551 are (apparently) unisexual is difficult to explain in the 
case of such sedentary animals as Cephalodiscus ; possibly 
the examination of a larger number of polypides from these 
specimens might result in the discovery of individuals differ- 
ing in sex from the majority, but I was loth to sacrifice for such 
B.1148. 
