286 ERNKS'r WARKEN. 



The view that a parthenogenetic tendency is favoui'able to 

 hybridism is also suggested by the fact that hybridism 

 appears to be especially easy in Echinoderms,^ and it is in 

 this group that the parthenogenetic tendency is strongly 

 marked and artificial parthenogenesis can be most easily 

 effected. Pseudogamy, or the stimulation of partheno- 

 gensis by the semen of the male, without real fertilisation, is, 

 in the case of insects, a phenomenon based, as far as I am 

 aware, on indirect evidence, and not on actual cytological 

 observation ; although in Echinoderms some evidence of 

 this nature has been adduced. 



In the observations above described there is undoubtedly 

 strong evidence that the females which were placed with the 

 male of another species behaved differently than when un- 

 paired, and the eggs were markedly affected. 



In the case of me nip pe ? x maia c?, the single larva 

 which hatched was so fundamentally similar to a noi*mal 

 menippe larva, that it would appear extremely improbable 

 that it was a hybrid arising from real fertilisation. The only 

 other alternative view which appears admissible is that 

 copulation occurred and that a spermatozoon entered the egg 

 and stimulated the normal parthenogenetic power without 

 actual fusion of the male and female pronuclei, or, possibly, 

 the mere contact of the male fluid acted as a sufficient 

 stimulus. It has been stated, but on whose authority I have 

 not ascertained, that painting the eggs of silkworms with 

 different chemicals stimulates parthenogenesis, and if such is 

 the case it could be readily understood that contact with the 

 male fluid might have an analogous effect. 



In one of the pairings, maia ? x belina J, the male 

 appears to have had an undoubted influence on the eggs, biit 

 without cytological evidence it is impossible to judge Avhether 

 or not there was true fertilisation, since development did not 

 proceed beyond early segmentation. 



1 See Shearer, C, Morgan. Walter D., Fuchs. H. M., " On the 

 Experimental Hybridization of Echinoids," ' Phil. Trans. Roy. Soc. 

 Lond.,' vol. cciv. 1914. 



