PHOLAS. 191 



observations on the anatomy of the Lamellibranchiata, I will 

 only at present mention the veins 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 inspissated 

 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 \iscous humour distilled from the veins 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 PJiolas 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 ligament, 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 Mactra, Mya, Lutraria, &c., which have internal 

 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 virile membranous 

 pouches, are distended and fully developed ; but in the winter 



