C. F. ROUSSELET ON PROALES WERNECKI. 417 



stout, almost globular, pointed at both ends (figured by Hudson 

 and Gosse, PI. XXXII., Fig. 18c). The ovary is greatly dis- 

 tended with a large number of immature eggs, and the stomach 

 filled with a very large mass of dark brown granulated undigested 

 matter. It is probable that the intestine and rectum have become 

 inactive, as no excrements are found in the galls, and the animal 

 has not been seen to discharge any. The experiments I have 

 made in this direction have all been negative. 



Some galls contain all female eggs, and others both female and 

 male eggs. The male eggs are somewhat smaller and far less 

 numerous than the female eggs. Fertilised resting eggs, slightly 

 larger, with double walls and smooth surface, are also found, but 

 I have not seen them. Professor Bothert figures the resting egg, 

 and states that he found as many as thirty to fifty-four of such 

 eggs in one gall, all laid by a single female. He is inclined to 

 think that the resting eggs are not the fertilised eggs because 

 they are nearly as numerous as the ordinary female eggs, and 

 because he saw them produced both when males were about and 

 when there were none. This, however, is not conclusive, as a 

 few males may have been present even if they were not seen. 

 M. Maupas' * experiments and researches a few years ago on 

 Hydatina senta went to show that the resting eggs were fertilised 

 male eggs (that is, eggs which, if they remained unfertilised, would 

 have produced males), that male eggs only were capable of being 

 fertilised, and that the ordinary parthenogenetic female eggs 

 were never affected by the presence of males. Fertilisation takes 

 place at an early stage, when the eggs are still in the oviduct or 

 even ovary. M. Maupas has further shown that each female 

 Hydatina lays one kind of eggs only, either female or male eggs, 

 and if the latter have been fertilised, instead of producing males 

 they become resting eggs. The animals issuing from the resting 

 eggs, after a period of rest more or less prolonged, are ordinary 

 females. The determining factor, according to M. Maupas, which 

 will produce a Hydatina laying male or female eggs is heat ; a high 

 temperature in the water, above 26° C, producing females laying 

 male eggs, and a low temperature females laying female eggs. 

 According to the same authority the egg is neuter quite at the 

 beginning of the oogenesis, and by lowering or raising the tem- 



* Maupas, " Comptes Rendus," tome cix. (1889), p. 270 ; tome cxi. (1890). 

 pp. 310 and 505 ; tome cxiii. (1891), p. 388.2 



