ZOOLOGY AND BOTANY^ MICEOSCOPY, ETC. 41 



the Chitons to Neomenia, in which he oj^poses the doctrine of 

 V. Ihering, that the former are derived from the latter, and holds 

 that the two are separately evolved groups, related only by the posses- 

 sion of a common ancestor. 



Generative Organs of Oysters.* — P. P. C. Hoek finds, as his most 

 remarkable result, that the generative organs of oysters are not 

 localized glands, but are distributed over the whole surface of the 

 body ; they are not separated from the integument on the sides of the 

 body, and in front of the pericardiac cavity there is a dorsal and a 

 ventral connection between the two halves of the organ. We every- 

 where meet with ramifications, which are in communication one with 

 another, and have the internal wall forming internal culs-de-sac ; the 

 epithelial cells of these are converted into eggs or spermatozoa, both of 

 which are produced from the same cell. The external longitudinal cleft, 

 described by Lacaze-Duthiers, leads into a genital canal, which begins 

 to ramify near the orifice ; the branches ramify afresh, and extend 

 over nearly the whole of the sui'face of the body. There is no trace 

 of any genital papilla, and the orifice serves also for the organ of 

 Bojanus. As to this last, the author states that it does not form a 

 very distinct organ ; it is comjiosed of intercommunicating mem- 

 branous folds, which open into a cavity lined by ciliated epithelium, 

 and leading by a small canal to the urogenital orifice. In the wall of 

 this cavity there commences a narrow canal, which runs almost 

 parallel to the genital duct, and opens into the so-called pericardiac 

 cavity. The author believes that the female products are often ferti- 

 lized before they escape, and that the oyster is not only morpholo- 

 gically but also physiologically dioecious. 



MoUuscoida. 



Early Development of Salpidae. t — F. Todaro, in his second 

 preliminary communication, states that he has found that the follicle 

 is divided into two sacs, which communicate freely with one another ; 

 one is at first much larger than the other, and may be known as the 

 ovarian sac, as it contains the ovum during the whole period of its 

 maturation ; the other is very small and empty, and appears as though 

 it were merely a small introflexion of the larger one. As the ovarian 

 sac diminishes, it grows in size, so as to be able to receive the ovum, 

 which remains in it during the period of segmentation. We may, 

 therefore, call it the embryonic sac ; it is provided with an organ of 

 attachment, by means of which it is able to attach itself when it 

 passes into the uterus. 



The author does not now go into detail with regard to the various 

 stages of the development of the ovum, but merely states that he has 

 observed the entrance of a single zoosperm, its conversion into a 

 male pronucleus, and its fusion with the female pronucleus to form 

 the segmentation-nucleus ; the nutrient material of the egg is 

 obtained from the epithelial cells of the ovarian sac. The same 



* Comptes Rendus, xcv. (1882) pp. 869-72. 

 t Arch. Ital. Bio]., ii. (1882) pp. 1-9. 



