BULLETIN OF THE UNITED STATES FISH COMMISSION. 405 



dula glauca), as observed by the writer. Some very singular figures of 

 the eggs of the European oyster in Poli's Testacea siciltie, published in 

 1795, renders it not improbable that he may have seen this singularly 

 formed nucleolus. 



The ova are not all " ripe " in all cases at the same time in the same 

 ovarian tubules. The same condition of affairs is found in the ovary of 

 the oyster as was observed in that of Scrobicularia by Von Jbering; 

 that is, while some ova were mature others in the same tubule or folli- 

 cle were still very immature. The condition of the ovary varies, how- 

 ever, considerably in different individuals; in some cases the most of the 

 ova are ripe at about the same time, in others there is a greater differ- 

 ence between the time of maturity of dilferent eggs. It is also frequently 

 observed that a portion of the generative organs of the same oyster are 

 much more advanced in maturity than other portions. The ovaries and 

 spermaries are never entirely wasted away or atrophied, as would ap- 

 pear to the naked eye. The full, enlarged appearance which is noticed 

 when the generative glands are full of ripe products is often due to a 

 distension of the ducts which lead away from the tubules or follicles, 

 and wheii this is the case, if the handle of a scalpel is gently stroked 

 over the distended ducts over the side of the animal, from its head end 

 towards the posterior portion below the muscle, the ova or spermatozoa, 

 as the case may be, can be forced out of the open end of the main effer- 

 ent generative duct into the upper gill chamber of its own side, into 

 which the former opens, as described in the anatomical outline sketch 

 given in my report to the Maryland commissioner for 1881, page 15. 



It has recently been asserted by some Dutch investigators that the 

 generative products were not discharged by way of a single duct on 

 either side of the animal, as described by Lacaze-Duthiers. What ana- 

 tomical grounds these observers have for this statement I do not know ; 

 they appear to have been investigating the structure of the animal by 

 means of thin slices or sections. Tlie simple experiment with a sexually 

 ripe oyster, as described above, has invariably given the same result ; 

 never more than a single opening was found on one side from which the 

 eggs were seen to issue. So far thin sections of the oyster as observed 

 by me have not shaken my belief in the accuracy of the observations of 

 Lacaze Duthiers, nor have I seen any evidence of three generative open- 

 ings and ducts on either side of the Euro])ean oyster, as asserted by 

 Davaine, nor is it worth while to more than notice Home's error with 

 regard to the water-chamber above the gills, which he regarded as the 

 oviduct. 



At the time the oyster is full of spawn, the generative organ completely 

 envelops the viscera (liver, intestine, and stomach) except a small por- 

 tion at the anal end of the intestine, and the head end of the visceral 

 mass. All of the deeper tubules or follicles composing the generative 

 gland trend towards, and join directly or indirectly the main duct on 

 either side of the body, into which they pour their products as the latter 



