THE DEVELOPMENT OF THE TEMNOCEPHALE^. 419 
the fonnation of the egg closely correspond. The two main 
vitelline ducts, right and left, open together into the oviduct 
near the ovary. Close to this the oviduct gives off a short 
branch leading to a larg’e sac, with a syncytial epithelium, 
lying near the middle line in front of the rest of the female 
apparatus. This has been very usually called the recep- 
taculum seminis — a name for which, in view of the fact 
that its contents consist very largely of yolk matter, I pro- 
posed (8) to substitute that of receptaculum vitelli. I 
was then of opinion that it serves as a receptacle in which 
yolk accumulates until enough has been collected for com- 
pleting an egg, when it is discharged into the ootype. A 
more thorough examination of the subject has shown me, 
however, that, at least as regards the Australasian forms, 
both names are inappropriate. The sac usually contains 
spermatozoa it is true, but they never form a large propor- 
tion of its contents ; and they are spermatozoa which have 
lost their activity, and move, when they move at all, with 
comparative sluggishness. It also contains yolk matter — the 
great bulk of the contents, in fact, consisting of that mate- 
rial, but it is yolkinatter which has undergone degeneration ; 
the cells have broken up, and the nuclei have, for the most 
part, disappeared. Moreover, mingled with the motionless 
or sluggish spermatozoa and the broken-down yolk-cells are 
shreds and strands of a substance which corresponds exactly 
in appearance and behaviour to staining agents with the 
secretion of the shell-glands. The conclusion to be arrived 
at from these facts is clear enough ; the so-called recep- 
taculum seminis, or receptaculum vitelli, is in reality a recep- 
tacle for surplus spermatozoa and surplus vitelline matter as 
well as shell-gland secretion. 
The question may suggest itself — What necessity is there 
for such a receptacle ? Why should the surplus matter not 
be passed directly out through the female duct ? To this the 
answer obviously is that very frequently — whenever, in fact, 
an egg is in course of formation in the ootype or is lodged in 
the distended atrium — the way to the exterior is blocked, 
