ZOOLOGY AND BOTANY, MICROSCOPY, ETC, 45 



the uterine vessels. Tliese influences are largely of a mechanical 

 character. 



The facts known to us seem to show that the amnion is the result 

 of the gradual invagination of the embryo into the blastodermic 

 vesicle ; and it is probable that the cavity of the false amnion is the 

 homologue of the cleavage cavity of certain of the lower forms. 



Sexual Dimorphism.* — Mr. J. Stolzmann, basing his views on a 

 study of birds, comes to the result that sexual dimorphism is often to 

 be explained as being due to natural selection ; where it is only feebly 

 marked we may believe that it is to be explained by the law of the 

 correlation of growth ; a female, externally, may be regarded as an 

 incompletely developed male ; the role of the female is more difficult 

 than that of the male, and the ovaries require a larger blood supply 

 than the testes ; this view is supported by the fact that old or sickly 

 females take on the male characters. 



Spermatogenesis of Bombinator.t — In continuation of his re- 

 searches on spermatogenesis, Prof. v. la Valette St. George describes 

 the structure and development of the spermatozoa of Bomhinator, 

 with a critical review of the relative literature. 



Structure. — The spermatozoon is a spindle-shaped body, ending 

 anteriorly in a clear blunt tip, and drawn out at the other end into a 

 fine process. Close to the anterior tip a filament is attached, which 

 runs alongside of the body, more or less separated from it, and con- 

 tinued beyond it. On this is borne the vibratile fringe, which does 

 not, however, extend the whole length of the filament. The vibratory 

 movements occur from the anterior end backwards to the fine point. 

 The whole spermatozoon is probably surrounded by an envelope of 

 protoplasm, the contractility of which is specially differentiated in 

 the fringe region. The forward movement of the sperm is rotatory, 

 produced partly by the spiral twistings of the vibratile membrane, 

 and partly by the worm-like bondings of the body itself. The 

 author maintains that the structure described is that of the perfectly 

 mature sperm. 



Development. — The development of the spermatozoa of Bomhinator 

 is in accordance with the author's previous results ; (1) spormato- 

 gonia surrounded by a follicular envelope (" FoUikelhaut") with nuclei, 

 divide with nuclear karyomitosis ; (2) the resulting spermatocytes 

 multiply in a similar manner and form masses termed spermatocysts, 

 surrounded by a cyst-envelope (" Cystenhaut ") with nuclei, perhaps the 

 same as the follicular membrane; (3) from the repeated division of 

 the spermatocytes, spermatides or undifferentiated sperms result, from 

 which by elongation of nucleus to form the body, formation of filament, 

 diminution of protoplasm, &c., the (4) mature spermatozoa arise. 



Influence of Saline Water on the development of Tadpoles.J — 

 M. E. Yung finds that a tadpole placed in sea-water of the Mediter- 

 ranean, which contains about 4 per cent, of salts, dies, shrivelled up, in 



* Proc. Zool. Soc. Loud., 1885, pp. 421-32. 



t Arch. f. Mikr. Anat., sxv. (1885) pp. 581-93 (2 pis.). 



j Comptes Kenclus, ci. (1885) pp. 713-4. 



