ZOOLOaY AND BOTANY, MICROSCOPY, ETC. 641 



The following method of investigation was adopted ; after removal 

 from the shell, the animal was thrown into a chromic acid solution of 

 from one to two per cent., and was so allowed to remain for several 

 days. After hardening satisfactorily, it was thoroughly washed and 

 soaked in water for two days, and finally put into alcohol. Thick 

 slices or blocks of the body should then be cut in a transverse direc- 

 tion, and it is as well to take several individuals, inasmuch as in any 

 two the sexual glands will hardly be found to have attained the same 

 state of maturity. After the blocks had been soaked in water for a 

 day, they were dried, and then placed in a solution of gum arable for 

 from 24 to 48 hours ; again covered with strong alcohol, they are, 

 after a day, hard enough to cut. The sections were found to be most 

 conveniently stained with the following reagent : equal parts of dense 

 alcoholic solutions of safranin red and methyl green are poured 

 together, and diluted with about eight times their combined volumes 

 of water. Being now too deeply stained to be at once mounted, the 

 sections must be transferred to 95 per cent, or absolute alcohol, and 

 stirred about in it ; as soon as the sections are of a rosy red hue, they 

 should be removed and placed in oil of cloves. If the process of 

 the extraction of the colour has been allowed to go on too long, the 

 staining effect of the safranin is lost ; while it will stain the eggs, the 

 methyl green only affects the spermatozoa and the cells from which 

 they are derived, " It is one of the most astounding facts known to 

 histological chemistry, that although both of these dyes, to begin 

 with, are intimately mixed together in the staining fluid, the different 

 histological elements of the section exert some kind of selective power 

 by which they absorb and hold mainly the one colour only." 



This elaborate method of investigation is only necessary for Ostrea 

 edulis, where the spermatozoa are packed together in oblong clusters, 

 which are often of about the size of the ovarian ova ; and this species 

 is essentially hermaphrodite, while 0. virginica and 0. angulata are 

 unisexual. It is further to be noted that, in the first, the calibre of 

 the generative tubules appears to be relatively greater than in the 

 other two species. 



The author enters into a detailed account of the results of his 

 observations, and concludes by discussing the evidence which we 

 have as to the annual regeneration and final abortion of the repro- 

 ductive organs of the oyster. Together with the changes in the 

 glands, there are remarkable changes in the solidity and consistence 

 of the animal ; " the shrinkage of a spawn-spent oyster in alcohol is 

 excessive, and may reduce the animal to one-tenth of its living bulk ; 

 this is, of course, due to the absorption of the water with which the 

 loose tissue of the exhausted animal is distended." It would seem, 

 therefore, to be clear that, in consequence of the enormous fertility 

 of the oyster, a vast amount of stored material in the shape of con- 

 nective tissue must be annually converted into germs, and annually 

 replaced by nutritive processes. 



The author thinks that there is, as yet, no conclusive proof of the 

 alternate activity of the generative organs in producing ova and 

 spermatozoa ; and though he recognizes that his view is in opposition 



