THE INTERNAL STRUCTURE OF THE OYSTER. 717 



translucent. In this condition, if the reproductive glands are undeveloped, the dark mass of 

 the liver may be seen through the body walls. Towards the autumn, on the other hand, the 

 connective tissue cells acquire a milky opacity and great solidity as compared with their watery, 

 transparent condition in summer. This last condition, which involves the whole mantle, the palps 

 and superficial portions of the visceral mass, indicates to the oysterman the condition of fatness. 

 The Oysters in this state are plump ; do not so readily diminish in bulk when removed from the 

 shell as in summer ; but that this change is due to storage of fatty matters I have not yet seen any 

 evidence of any sort which would amount to proof. There is some oily matter in the Oyster, but 

 not enough to account for the changes which we have described. 



The atrophy of the connective tissue during the summer season would appear to indicate that 

 the material for the genesis of the reproductive elements was derived from the mesenchyme, by a 

 direct transformation of its substance in which the generative follicles are imbedded. It is, in 

 fact, the great development of the mesenchymal substance in the autumn and winter, when the 

 reproductive function is in abeyance, that constitutes the condition of the animal known to oyster- 

 men as fatness. These relations illustrate very beautifully a well-known physiological principle, 

 viz, that nutritive processes are very intimately related to the reproductive; they are in fact inter- 

 dependent. 



In summer, when the reproductive organs are gorged with their products, their follicles are 

 crowded together into contact; in winter, in their atrophied condition, they lie imbedded in the 

 superficial portion of the mesenchyme of the body-mass, the same as in summer, but are much 

 less developed, so as to appear in sections like a very open network of strands of very small, 

 nucleated, incipient embryo cells, the connection of which may be traced into the now collapsed 

 and internally ciliated branches of the oviducts. All the parts of the reproductive apparatus are 

 therefore present in winter, but in an undeveloped condition. The oviducts branch and spread 

 over each side of the body-mass just outside of the stratum of reproductive follicles and imme- 

 diately beneath the mantle. They do not ramify through the substance of the reproductive organ, 

 but traverse its surface, the follicles emptying their contents into the ducts by way of openings 

 upon the inner faces of the latter. The main openings of the oviducts of either side open into the 

 upper branchial cavity on either side of the hinder and ventral portion of the body-mass just 

 below the muscle. There is but one opening on either side, notwithstanding the various state- 

 ments to the contrary. 



Embryologically considered, the liver is an endodermal structure, a diverticulum of the 

 stomach. The great bile ducts pass outward from the cavity of the stomach and subdivide again 

 and again and end blindly in spacious ovoidal hepatic follicles, the simple plicated walls of which 

 consist of hepatic cells. The function of the liver is in all probability both excretory and secretory, 

 and takes an all-important share in the processes of digestion. That the function of the liver is 

 partially excretory is rendered all the more probable from the fact that there is little or no 

 evidence of the existence of a renal apparatus or organ of Bojanus in the Oyster such as is found 

 in other mollusks. Dr. Horst looked in vain for a rudiment of this last structure in the embryos 

 of Ostrea edulis. Transverse sections through those portions of the body where it would most 

 likely be found, made from both native and foreign examples, exhibit no structure in the least 

 degree resembling what is regarded as the organ of Bojanus in Unio and Anodonta. 



The wall of the intestine, like that of the stomach, is ciliated throughout, and is also of endo- 

 dermal or hypoblastic origin. Its wall is folded inward along one side in a peculiar way, so that its 

 lumen is more or less crescentic in cross-section. This arrangement, together with the very minute 

 minor folds on its inner surface composed of long, columnar, ciliated epithelial cells, increases the 



