ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 963 



group ; he adopts tlie method of formulation, on which he has already 

 written, and discusses in great detail the species found in this large 

 collection. 



Coelenterata. 



Development of Hydridse.* — Prof. A. de Korotneff has made a study 

 of the ova of Myriothela. He finds that the egg arises from a primordial 

 cell of ectodermic origin ; this cell gives rise to secondary germinal 

 elements, of which there are more than twenty ; of these one alone 

 produces the true germinal vesicle, while the nuclei of the other 

 elements disappear without leaving any trace behind them ; the nuclei 

 of the vitelline cells are converted into fatty or vitelline globules, and 

 all this mass of cells collects and forms a common mass which possesses 

 one germinal vesicle. From this point of view the egg itself ought to 

 be considered as an agglomeration of elements, the functions of which 

 are very different ; one of the secondary germinal cells gives up its 

 nucleus to the egg, and this serves as the germinal vesicle, the other 

 germinal elements produce the formative plasma of the egg, while the 

 rest gives rise to its vitelline parts. At the same time, each of these 

 three kinds of elements takes part in forming the plasma of the egg. 



The mode of origin of the male sexual products is altogether similar 

 to that of the females. Fecundation appears to be effected by the 

 penetration of spermatozoa into the peduncle of the egg. 



Metschnikoff has thrown doubt on the author's earlier account of the 

 remarkable mode of development oi Myriothela, but later observations have 

 convinced Prof. Korotneff that he was quite correct. The free ovum, 

 fixed by its peduncle, has no envelope whatever ; after a short time, 

 however, one appears, which may be regarded as a vitelline membrane ; 

 it is delicate, yellowish, and fairly resistent. As Prof. AUman discovered, 

 the median part of Myriothela produces long delicate filaments with 

 small tentaculiform heads at their free extremities. When the vitelline 

 membrane is formed, three or four of these heads attach themselves and 

 hold the egg in a certain position. At the same time the connection 

 between the egg and its stalk diminishes, the egg separates from the stalk 

 and remains fixed to the animal by the filaments. Analogous phenomena 

 may be observed in fresh-water Bydrse. 



In the egg itself there may be distinguished a central, finely granular 

 mass, a cortical layer altogether devoid of ectoplasmic vesicles, and 

 vitelline globules or modified nuclei, which are found in the endoplasm 

 only. Of the succeeding stages, some only were seen. There is an 

 active multiplication of the embryonic cells of the ovum, and a morula 

 results. The internal mass forms the endoderm, and this primitive 

 endoderm is not, as in most Arthropods, replaced by a secondary 

 endoderm. 



Flabellum.f — Dr. G. v. Koch has made a close examination of the 

 arrangement of the septa in Flahellum Michelini and F. pavoninum. Both 

 species afford, in his opinion, ideal examples of a law previously 

 enunciated by him, viz. — In the Hexacoralla every new septiim arises in 

 the space between two that are older, and the septa of every cycle are 

 nearly of the same size. There may be occasional exceptions, and these 

 are due to changes in the general growth. 



* Arch. Zool. Exper. et Gen., vi. (1888) pp. 21-31 (2 pis.), 

 t Morpliol. Jabib., xiv. (1888) pp. 329-14 (1 pi.). 



