262 PARTHENOGENESIS VII 



"the Parthenogenetic Eeproduction in Apus and 

 allied Crustacea." illready, in 1856, Siebold had 

 stated his supposition that Ajyiis cancriformis, Lim- 

 nadia gigas, and Polyphemus ocidus, in which species 

 no males had been observed, presented examples of 

 true parthenogenesis, and were not to be regarded as 

 bud-producing " nurses," in a so-called alternation of 

 generations. Leuckart subsequently expressed the 

 same opinion with regard to the reproduction, inde- 

 pendent of males, observed in Daphnia, Apus, and 

 Limnadia. Ever since that period Siebold has con- 

 tinually kept an eye upon Apus. In 1858 the males 

 of Apus were discovered by Kozubowski, and Siebold 

 received specimens from various localities. He thus 

 learned to distinguish with perfect facility the two 

 sexes, and w^as enabled now to convince himself that, 

 as with the Lepidoptera above spoken of, so with 

 Apus, broods occur which are entirely destitute of 

 males, and go on reproducing parthenogenetically, 

 whilst other broods occur in which both sexes are 

 present. The number of Apus of two species — Apus 

 cancriformis and Apus j^^^oductus — examined by 

 Siebold, amounts actually to some thousands. He 

 received quantities taken from various ponds in middle 

 Europe (Apus occurs in shallow pools which dry up 

 during parts of the year, and it can be taken in 

 immense quantity), and had the opportunity of study- 

 ing one pond — that at Gossberg, near Munich, with 

 minuteness, from the year 1864 to the year 1869 

 inclusive, besides casual examinations of the same 

 pond in 1857 and 1858. Time after time, taking 



