i86 THE PHYSIOLOGY OF REPRODUCTION 



formation does not take place, and the chromosomes are unable to 

 take up their proper position in the cell for division. 



In the frog it has long beea known that the future axis of the 

 embryo is determined by the point of entry and path of penetration 

 of the spermatozoon, the head of the future embryo appearing 

 approximately opposite the point at which the sperm has entered the 

 ovum. Thus the future bilateral symmetry of the larva is established 

 in the ovum before the germ nuclei have united by the path along 

 which the sperm head penetrates the cytoplasm of the egg, in order 

 to reach the female pronucleus. 



Another change brought about in some eggs by fertilisation has 

 been shown by certain experiments of F. Lillie.^ He has demonstrated 

 that the unfertilised eggs of the Polychfet Nereis and those of the 

 sea-urchin Arbacia contain some substance that rapidly agglutinates 

 the sperm of their own species. If watery extracts are made from 

 the unfertilised eggs of these animals, the addition of a little of 

 these extracts to their sperm suspended in sea-water results in 

 their agglutination within a very short time, but similar extracts 

 of fertilised eggs are without any action when added to sperm 

 suspensions. He also found that extract of eggs treated with various 

 chemical agents such as would induce artificial parthenogenesis, was 

 also without any action iu this respect. Bataillon^ has drawn 

 attention to the fact that the eggs of the frog after fertilisation are 

 resistant in a high degree to the cytolysing action of hepato- 

 pancreatic fluid. If a number of eggs of Banafusca are inseminated, 

 and are then treated in this manner, it is found that about two- 

 thirds of their number subsequently segment in an abnormal 

 manner, but one-third fail to divide and swell up and are cytolysed. 

 It is found on investigation that these eggs are the ones that have 

 failed to become fertilised. 



In the Mammalia fertilisation takes place usually in the upper 

 part of the Fallopian tube. 



The Oxidation Pkocesses of the Ovum on Feetilisation 

 AND During Early Development^ 



Loeb was the first to advance the view that the process of the 

 fertilisation of the ovum was one mainly concerned with oxidations 

 taking place in the egg, initiated by the entrance of the sperm. 

 Warburg * was able to show that this was definitely the case. The 



' Lillie (F.), Problems of Fertilisation, Chicago University Press, 1919. 



2 Bataillon, " Nouvelle contribution a I'analyse exp6rimentale de la f 6conda- 

 tion par la parthenog6nfese," Anns. Inst. Pasteur, vol. zxx., 1916. 



' By 0. Shearer. 



* Warburg, " Beobachtungen tiber die Oxydationsprozesse im Seeigelei," 

 Zeitsch.f. Physiol. Chem., vol. Ivii., 1908. 



