420 
^V. A. HASWELL. 
and in order that the foi’mation of the egg may proceed 
without interference, the yolk-cells which are being dis- 
charged into the oviduct, and the shell-gland secretion which 
collects after the shell has become formed, as well as the 
surplus spermatozoa, have to be disposed of. 
That this is the function discharged by the receptaculum 
in Temuocephala there remains, to my mind, not the 
slightest doubt. The function of a true receptaculum 
semiuis in those animals is discharged by the anterior 
part of the oviduct, in which a mass of actively moving 
spermatozoa is usually to be found. T. comes has an excep- 
tional aiTangement of the parts ; in that species the cavity of 
the receptaculum is incompletely divided into two unequal 
parts by a partition which is pierced in the middle by a wide 
aperture. In all the specimens I have examined, while the 
distal larger part of the cavity, the part furthest from the 
oviduct, is filled with the usual mixture of effete genital 
products, the smaller part is occupied by a mass of normal 
spermatozoa. 
Whether the relatively large sac known as receptaculum 
seminis in other Platodes may perform in some cases the 
same function as that above ascribed to it in Tern no- 
cep lial a is a question worthy of further investigation. 
Where, as in many Distomids, a Laurer’s canal is present 
that canal seems to be the natural outlet for the unused and 
effete materials; when as in Distomum nodulosum, 
D. globiporum, D. isoporum, and others (Looss, 11), a 
receptaculum is present as Avell, it may act as a true recep- 
taculum seminis. When a Laurer’s canal is absent the 
receptaculum in some forms — D. variegatum (Looss, l.c.) — 
contains yolk-cells as well as spermatozoa. Looss expresses 
the opinion that, in general, the spermatozoa contained in 
the receptaculum semiuis of Distomids aie in process of 
dissolution, and no longer capable of effecting fertilisation. 
If this be true of the Distomids as well as Temn ocephala, 
it is at least possible that the same may prove to be true of 
the other groups — Polyclads, Heterocotylean Trematodes. 
