HOTIFERA. 305 



kinds, large and small. The large develop into females, and the 

 small into males; they are produced by different individuals. Asexual 

 reproduction is unknown. 



It has been established by Maupas* that in certain Rotifera 

 (Hydatina senta) the same animal produces only eggs of^bne sex; 

 thus, a female which has once laid the small male egg never produces 

 a female egg, and vice versa. He has further shown that while 

 the general rule is that female eggs should be produced a rise 

 in temperature, if applied at the earliest stages of their short life, 

 will ensure the production of the small male eggs. Further, he has 

 shown that the layers of female eggs are devoted to parthenogenesis, 

 and only produce the thin-shelled immediate eggs. Copulation of 

 such with a male has no effect. On the other hand copulation 

 between a young female, which would, if left alone, lay only male 

 eggs, and a male brings about a complete change in the character 

 of the eggs ; in this case the egg acquires a thick, hard, often orna- 

 mented shell, and develops immediately to a certain stage ; but the 

 development soon ceases and the egg becomes a resting so-called 

 winter egg. Such eggs may be produced at any season of the 

 year, and their peculiar property is to be able to resist drought 

 and other adverse influences ; they give rise only to parthenogenetic 

 females, which lay thin-shelled immediate eggs. Finally, copulation 

 between a male-producing female, in which the eggs have been 

 formed, and a male has no effect; in such a case the female lays 

 small immediate eggs, which develop at once into males. 



It thus appears that, as in the bees, an egg which would, if 

 fertilized, produce a female, will, if not fertilized, produce a male. 

 Should these most important and interesting observations be con- 

 firmed and here it may be observed is a subject of the most 

 fascinating and far-reaching character for research it would appear 

 that in the Rotifera the problem of how to control the production 

 of the sexes has been solved. 



The development has been studied in the parthenogenetic imme- 

 diate eggs. It throws no light upon the affinities of the group. 

 The young are hatched with practically the form of the adult. 

 There is said to be no mesoderm in the ordinary sense of the 

 word, but the rudiments of the organs are laid down independently. 



The Rotifera principally inhabit fresh water, but marine forms 

 are known. Some species live in gelatinous tubes which they 

 secrete, or in a case consisting of pellets manufactured by the animal 



* Ccmiptes rendus Acad. Sci., 109, 1889, 90, 91. 

 X 



