$^ M. Prevost o}i the Generation of Animals. 



the disposition of these to be such, that the animal cannot fe- 

 cundate itself, and even that mutual impregnation between two 

 individuals is impossible. To complete the purpose of nature, 

 the animals require to arrange themselves in lines or chains 

 in a certain position, so that the sexual organs may be in 

 contact, one with the male organ in connection with the oviduct 

 of the nearest adjacent animal on one side, and its own oviduct 

 in a position to be impregnated by a third individual. In the 

 ditches where they abound may often be seen long chains 

 of these animals, in which, with the exception of the two at the 

 extremities, all are alternately fecundated or fecundating. 

 This memoir has also an illustrative engraving. 



The third memoir, on the generation of the Midus gobio, 

 contains the result of the investigations of MM. Dumas and 

 Prevost on this subject, which have led them to conclude, that 

 the principal phenomena of generation among fishes is identi- 

 cally the same with what takes place in the other vertebrated 

 animals. Fecundation is accomplished as among the Batra- 

 chian reptiles ; that is, at the moment when the ova leave the 

 oviduct the male discharges the spermatic fluid into the wa- 

 ter. The ova which fall into this medium absorb a portion, 

 and the current which results from this absorption carries the 

 animalcules to the surface of the ova. " I verified this fact" 

 (says M. Prevost) " by taking an ovum from the oviduct and 

 placing it in spermatized water. If at this moment it be ex- 

 amined with the microscope, the animalcules are seen carried 

 to the periphery of the ovum by a strong current, and the foetus 

 rarely fails of developing itself. It is necessary to the success 

 of the experiment, however, that the impregnated ovum be 

 placed immediately in running water. The foetus is seen, as 

 amono- birds, in the centre of the cicatricida, under the figure 

 of a spot inflated at one of its extremities, and slightly narrowed 

 at the other, which is the posterior one. The contents of the 

 ova in these animals is analogous in chemical composition to the 

 yolk of the eggs of the common fowl and the corpora lutea in 

 the ovary of the cow. As in them there is found much albumen, 

 and a thick yellow oil soluble in ether ; and they differ chiefly 

 in containing no gelatine, but some traces of mucus. The 



