ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 423 



which convey the peculiarities of the parents. During the develop- 

 ment or the maturation of the genital products, as well as in the copu- 

 lation of the male and female nuclear substances, there is no breaking 

 up, but only change in form. The bearing of polyspermy and of 

 isotropy of the egg on this view is pointed out. 



The third chapter of the essay deals with the relations in which 

 nuclear substance and protoplasm stand to one another ; the nucleus 

 is regarded as being more highly organized substance, and as repre- 

 senting a special centre of force in the cell. 



Influence of external conditions on the development of Ova.* — 



This has been the subject of a series of observations by Drs. Rauber 

 and Sachsse. 



As regards temperature it was found (working with ova of trout, 

 salmon, frog, and fowl) that the maximum, minimum, and optimum 

 vary with different animals. The influence of temperature varies 

 further with duration. The age of ovum and larva made no per- 

 ceptible difference. An atmospheric pressure of three atmospheres, 

 continued for three days, stopped development, but did not cause death. 

 A constant pressure of eight atmospheres, on the other hand, not only 

 interrupted development, but altered the eventual shape of the embryo, 

 contracting the length and increasing the breadth and height. A 

 pressure of three-quarters of an atmosphere had no effect, but below 

 that, the embryos died. The influence of acid solutions on developing 

 eggs is also recorded, but nothing new was observed of scientific 

 interest, except the action of oxygen in quickening the development 

 of the regions near the gill-slits. 



Foetal Appendages of Mammals-f — The observations by MM. E. 

 van Beneden and C. Julin here recorded were made on rabbits and 

 bats ; they find that no amniotic covering is formed at the cephalic 

 end of the embryo of the rabbit ; the proamnion or portion formed by 

 the epiblast and hypoblast is temporary, and diminishes as the embryo 

 retires into the true amnion. The formation of a proamnion depends 

 on the anterior edge of the blastoderm remaining diblastic, or not being 

 invaded by mesoblast. The membrana pellucida disappears early and 

 is never villous. 



The investigations of Kupffer and Selenka have shown that there 

 is not, as has been supposed, any real reversal in the relative position 

 of the germinal layers of various rodents ; the present writers bring 

 the results of other embryological studies into associati(m with their 

 own, and conclude that the determining cause of the formation of the 

 amnion is to be found in the descent of the embryo, due to the weight 

 of the body ; the apparent reversal of the layers, and the formation of 

 a proamnion is due to the precocious descent of the embryo. 



Development of the Coelom and Coelomic Epithelium of AmpM- 

 bia-J — Prof. B. Solger is of opinion that the causes of the changes in 

 the coelomic epithelium are not to be sought for in the blood, but iu 



* SB. Gesell. Naturf. Frennde Berlin, x. (1884). 

 t Arch, de Biol., v. (1884) pp. 369-434 (5 pis.). 

 X Morphol. Jahrb., x. (1885; pp. 494-528 (2 pis.). 



