PHOLAS. 19] 
observations on the anatomy of the Lamellibranchiata, I will 
only at present mention the ves and glands which I think 
produce the cartilage and ligament. On carefully opening the 
lateral cavities on each side the anterior dorsal range, a fasci- 
culus of veins may be seen deposited therein, some of which I 
have traced to the liver ; and it is probable that the mspissated 
fluid thrown off by them is specially applicable to the formation 
of the cartilage and internal portion of the ligament, as I have 
found their excretory ducts to be spongy masses that send 
forth the viscous humour distilled from the ves on the in- 
ternal convex circular areas in which the valves articulate ; 
and a proof of one at least of the true uses of the excretory 
apparatus is, that in Pholas dactylus the fluid is of a light 
brown or drab, and it produces two thin cartilaginous plates 
of those colours, whilst in P. parva the colour is as dark as 
tar, and the plates of the cartilage correspond with it. It is 
probable the coarser parts of this secretion are separated from 
the concentrated cartilaginous matter, and form the interior 
layers of the hgament, the mantle only producing the external 
skin. It is reasonable to suppose that all bivalves have these 
secreting organs; and it will be desirable to ascertain if such 
shells as the Mactre, Mye, Lutrarie, &c., which have mternal 
cartilages of considerable volume, have the excretory and 
secretory organs correspondently developed as in the Pholades ; 
and if in those genera that have external cartilages, there is 
any variation of structure, 
The Reproductive Organs. 
The Acephala are hermaphrodites without congression, and 
as it is termed, they suffice for themselves; but this fact must 
not be understood ideally, as these animals have distinct visible 
organs, the union of which, within themselves, produces the 
male and female influences. I hesitate to concur in the state- 
ment of some authors, that the sexes are distinct in the 
bivalves. I think it is probable that this idea has arisen from 
the animals being examined at different periods of the year. 
In the genial months, the ovaria, and the vinle membranous 
pouches, are distended and fully developed ; but in the winter 
