PHOLAS. 187 
The spaces lining the roof of the anal siphon consist of four 
longitudinal rows; the two middle ones are the largest, and 
form transverse parallelogrammic figures, whilst the other two, 
one on each side, are smaller subquadrangular areas. I can 
conceive no other use for these crypts, in such families as have 
them, than as depositaries for the ova; if so, the oviducts of 
course communicate with them, and the ova probably remain 
there some time after fecundation ; and the final ejection, m 
bivalves of this structure, can only take place from the anal 
tube. It is probable that the principal use of the anal conduit 
in the bivalves, in which the branchial cavity is completely 
cut off from the anal one, is to receive the rejectamenta, 
supply water to the ova during their maturation, and ulti- 
mately to eject them™*. 
It is necessary to state that these experiments require much 
patience and attention, and some delicacy of manipulation, to 
arrive at sound results : it is very material not to use specimens 
with accidental lesions, or those made in removing the animal 
from the shell, which operation, from the obstruction of the 
crotchets, cannot be effected without some practice and dex- 
terity. 
The result of the 1st and 3rd experiments would appear to 
demonstrate the non-communication between the branchial 
and anal siphons in the Pholades ; this fact beg established, 
they will not be the exceptions; but it is probable that the 
Myade, Solenide, Lutrarie, &c. have a similar configuration 
of the branchial apparatus; and though the Veneres, Cardia, 
and other open-mantle bivalves have the character of their 
branchial saes different from those of the Pholades, in not 
having the siphons completely separated, but more or less 
confluent, the possibility of branchial currents must be ad- 
mitted. Still, as it has been shown that in the Pholades the 
water cannot be received and discharged otherwise than 
through the branchial aperture, or from the pedal orifice, it 
* Since this was written, doubts have arisen whether the ova after 
exclusion are deposited for a time in the crypts of the anal tube, or in the 
branchiz ; we have never discovered any out of the ovarium.—Exmouth, 
1853. 
