ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 665 



of eacli testicular follicle soon begin to diyide into smaller cells, and 

 the spermatozoa appear in the centre of the follicle, whence they 

 extend peripherally until at last there are only one or two layers of 

 large cells, the rest of the space being occupied by smaller cells, and 

 the free spermatozoa ; the head of these last is pyriform. 



In Pelagia voctiluca it was observed that the rudiments of the 

 generative organs were laid down very early, in the form of four bands, 

 set beneath the gastric filaments ; on one side of each band the cells 

 are thickened to form a germinal epithelium ; as soon as the products 

 have attained a certain size they pass into the supporting lamella, 

 which, at last, becomes completely filled with them. 



The chief result of these investigations is to show that, among the 

 Discomedusas, the Ephyridae alone present an exception to the mode 

 of development and structure which is found to be common to all the 

 rest ; while there are certain Ephyridte which can be altogether 

 brought into association with the other members of their family 

 — e. g. Collaspis acMllis. 



In the present state of oiu' knowledge we cannot derive the gener- 

 ative organs of the Discomedusfe from those of the Ephyridfe ; these 

 organs in the latter group would appear to be independent fonn- 

 ations ; and this being so it is possible that Haeckel is not justified in 

 regarding the Ephyrid as the primitive form of the Discomedus^e. 



Hamann's second essay deals with the development of Tiara 

 pileata ; the ova are devoid of any membrane, segmentation takes place 

 with extreme rapidity, and cleavage is quite regular. The gastric cavity 

 of the gastrula is an elongated slit. The observations made on this form 

 bring to mind those of Claus on ^quoreaforslialea, and seem to show 

 that there is a direct connection between the processes of invagination 

 and delamination in the formation of the gastrula. 



Reproduction of Hydroid Polyps.* — A. de Yarenne here gives a 

 full account of his work.| Having studied the develoj)ment of the 

 ovum in a number of species, some of which had fixed sjDorosacs, some 

 fixed gonophores, and some free-swimming gonophores, he finds that, 

 in all, the ovum arises from a cell of the diflerentiated endoderm 

 of the coenosarc of the polyp ; all intermediate stages may be observed 

 between the ordinary endodermie cell and a well-developed egg-cell ; 

 the differentiated cells pass into a bud which, at first, is nothing more 

 than a csecal diverticulum of the body of the polyp ; the differentiated 

 cells thither conveyed become united into groups. Occupying the 

 endoderm of the diverticuluxQ, they are in direct contact with the 

 gastro-vascular cavity. The diverticulimi grows and finally becomes 

 a sporosac, a demi-medusa, or a fi"ee medusa. Experiments have shown 

 that it is the presence at certain points of a certain number of ovules 

 that determines the formation at these points of gonophores or 

 medusae ; and that, far from being anterior to the ova or spermatozoa, 

 the gonophores are posterior to them. It seems to the author that, if 

 the generative products arrive in the gonophores in an already 



* Arch. Zool. Exper. et Gen., x. (1882) pp. 611-710 (10 pis.). 

 t See this Jourual, ante, p. 72. 



