Hermaphroditism among the Apodidfe. 305 



gradually with mere periodical swellings. May we not assume 

 that the failure to form the typical branchings indicates a 

 lack of nutrition, one result of which is that the cells which 

 here, under more favourable conditions, might have pro- 

 duced eggs, divide up into sperm-cells? The evidence, 

 therefore, certainly points to a normal hermaphroditism 

 among the arctic Apodidse. With regard to the more 

 central European species, both the hermaphrodite specimens 

 of L. productus and of Apus cancriformis above described 

 were apparently suffering some privation in the way of 

 nourishment, if we may judge from the generally collapsed 

 condition of the immature eggs ; while, further, the con- 

 dition of the alimentary canal of the specimen of Apus cancri- 

 formis clearly indicates a state of semi-starvation. 



In these facts, then, it seems that we have some indications 

 of the conditions which induce hermaphroditism. It appears 

 that the Apodidae which, under favourable circumstances, 

 produce parthenogenetically, may become hermaphrodites 

 when food is scarce. This hermaphroditism is thus super- 

 imposed upon the parthenogenetic females. 



On comparing this with observations which have been 

 made on kindred forms, interesting speculations are suggested 

 as to the relations of these hermaphrodites to true males. 

 The males of different families of Cladocera begin to appear 



when the year is waning and food is getting scarce. Kurz 

 found that the males of Daphnia always appeared whenever 

 the puddles began to dry up, and he even succeeded in some 

 cases in producing males artificially by slowly draining off 

 the water in which the animals lived. This observer, on 

 accidentally finding hermaphrodite specimens of four distinct 

 species just about the time when the males begin to appear, 

 suggested that such were probably of frequent occurrence and 

 that this might be a sort of provisional arrangement. The 

 needed males were not immediately forthcoming, and herma- 

 phroditism tided over the interval. 



Kerhervd's observations led to the same conclusion ; not 

 only do males appear on the advent of " hard times," but the 

 females undergo a change. " Quelques jours suffisent pour 

 transformer une Daphnie parthe"nogene*tique, indifferente aux 

 males en femelle ephippiale douee d'affection sexuelle, en 

 pondeuse d'oeufs destines a etre fe*condes. Le facteur prin- 

 cipal de cette modification, ici je le repete, est la penurie des 

 vivres " |. 



* Kurz, " Ueber Androgyne Missbildung bei Cladoceren,"' SB. Akad. 

 Wien, lxix. Abth. i. 1874, p. 40. 



t Mem. Soc. Zool. de France, v. p. 227 (1892). 



