ZOOLOGY AND BOTANY, MICKOSCOPY, ETC. 359 



and, where sucli are present, the processes of the spermatozoon ; it 

 either remains capable of amoeboid movement or unites with the 

 nucleus to form a ciliated cell. In many cases the rudiment of the 

 investment of the " head " or of the median portion may be recognized 

 as a secondary nucleus or a thickening in the protoplasm of the sper- 

 matocyte. This investment of the head does not play any essential 

 part in fertilization, and is, indeed, ordinarily got rid of before the 

 spermatozoon passes into the egg ; when it does pass into the egg it 

 becomes mixed up with the yolk like the other parts of the seminal 

 body that are derived from the protoplasm of the spermatocyte. 



Development of Spermatozoa.* — A. Swaen and H. Masquelin 

 contribute a short abstract of results derived from a study of the 

 development of spermatozoa; the types investigated were certain 

 Selachians, the salamander, and the bull. The epithelium of the 

 testicles of these animals is formed by two distinct types of cells, 

 (1) " male ovules," (2) cells of the follicles ; the former give rise to 

 the spermatozoa in the following way : each of the cells divides and 

 forms a number of small cells — the spermatocytes, which always 

 remain united by a portion of the protoplasm of the mother-cell 

 which persists as intercellular substance ; the whole group of sperma- 

 tocytes may be termed a spermatogemma ; the spermatocytes are 

 gradually metamorphosed into spermatozoa, being termed in the inter- 

 mediate stages nematoblasts, the spermatogemma becoming therefore 

 a nematogemma. During the course of development the sperma- 

 tocytes and especially the nematoblasts are grouped in different ways, 

 varying in the different types of animals studied, but finally unite 

 into bundles of spermatozoa, in which all the elements are arranged 

 parallel to each other. 



The follicular cells form an envelope, which may be more or less 

 complete and last for a longer or shorter time, to the male ovules 

 and the spermatogemmsB ; later they become fused with the inter- 

 cellular substance of the nematogemma, and are no doubt actively 

 concerned in the varied grouping of the nematoblasts, and also in the 

 expulsion of the completely developed spermatozoa. Comparing the 

 development of the spermatozoa and ova, the following similarities and 

 differences may be noted ; in both there is an ovule surrounded by a 

 more or less complete layer of follicular cells ; in the ovary this cell 

 developes at once into the ovum, and the follicular cells multiply 

 actively ; in the testicle the ovule developes by indirect division, while 

 the follicular cells hardly multiply at all, and more often increase 

 in size. 



The paper concludes with a more detailed description of the 

 process of development in the several types. 



Human Embrycf— H. Ful makes an important contribution to 

 our knowledge of the structure of the human embryo, obtained 

 from the study of an embryo 5-6 mm. in length and probably about 



* Bull. Acad. K. Belg., vii. (1884) pp. 42-51. 

 t Arch. Sci. Pliys. et Nat., xi. (1884) pp. 93-5. 



