U<*, FERTILISATION 237 



which is opposed to Loeb's interpretation of the observed phenomena. 

 This investigator has shown that it is possible artificially to fertilise 

 sea-urchins' eggs by treating them with solutions of tannin and 

 ammonia. He had already formed the conception that the essential 

 facts of cell division could be resolved into a succession of processes 

 involving coagulation and liquefaction. The formation of the 

 vitelline membrane is said to be essentially a coagulative process 

 (and also possibly the formation of the centrosome and of the nuclear 

 spindle), and the dissolution of the nuclear membrane and certain 

 of the accompanying events are regarded as evidence of liquefaction. 

 These considerations led Delage to employ tannin as an agent for 

 inducing coagulation, and ammonia for causing liquefaction. Tannate 

 of ammonia was found to produce a similar effect, but this is 

 explained by Delage 011 the assumption that, since tannin is a feeble 

 acid and ammonia is a feeble base, the ammonium tannate becomes 

 dissociated, so that the acid function (which brings about coagulation) 

 and the alkaline function (which causes liquefaction) may be supposed 

 to coexist in the solution, and so separately to exert an influence on 

 different parts of the egg. By adopting the above-described method, 

 Delage succeeded in artificially fertilising ova, so that they developed 

 into complete sea-urchins, but it is curious to note that the symmetry 

 of these individuals was liable to be abnormal, one of them being 

 hexameral instead of pentameral. Delage also obtained successful 

 results by using carbon dioxide and other agents, and starfishes' eggs 

 as well as sea-urchins' were successfully fertilised. Furthermore, 

 certain of the experiments seemed to indicate that the presence of 

 oxygen is not an important factor (as supposed by Loeb), since develop- 

 ment could be induced after the oxygen present had been very largely 

 eliminated (but see pp. 186-197). 



It is, of course, obvious that Loeb's interpretation of the observed 

 phenomena of fertilisation among the Metazoa is inapplicable to the 

 process of gametic union in the Protozoa, in which the conjugating 

 units are often apparently similar and equipotential, and the same 

 objection may be offered to Delage's theory. It is possible, however, 

 that conjugation in the Protozoa, while presenting an essential 

 similarity to fertilisation in the Metazoa, initiates a series of chemical 

 processes of a relatively simpler kind. Moreover, the theory that 

 the changes consequent upon gametic union are the result of a 

 catalytic chemical reaction is in no way opposed to the vaguer 

 physiological conception that the object of the process is to secure 

 a rejuvenescence of vital substance without which the race cannot 

 . be perpetuated. 



The cytological changes which occur in artificially fertilised ova 

 have been dealt with at considerable length by Wilson, to whose 



