PACKARD.] PHYLLOPOD CEUSTACEA OF NORTH AMERICA. 615 



similar to the ovisac of the young BrancMpus feroc^, Gr. lu such old 

 males, the spermatic particles are very clearly enlarged. How far these 

 changes could go on, he could not say, since this BrancMpus is short-lived. 

 Tbese changes in the sexual organs are especially marked in old indi- 

 viduals; and he further remarks that such misshapen forms often 

 occurred in the salt-jwols after heavy rains." (Siebold and Kolliker's 

 Zeitschrift, 1872, p. 293.) 



Such facts as these show how desirable collections in very large num- 

 bers, at different seasons of the year, and from different localities, are 

 for the proper study of these animals. Moreover, they are among the 

 most important facts showing how new generic and specific forms, as 

 well as an unusual mode of a sexual reproduction, arise in consequence 

 of changes in the physical surroundngs of animals. 



Von Siebold, in his second work on parthenogenesis, has ascertained 

 that Apus also reproduces by this virgin reproduction. Already, in 

 1856, Siebold had stated his supposition that Apus cancriformis, Lim- 

 nadia gigas, and Polyphemus oculus, in which species no males had been 

 observed, presented examples of true ijarthenogeuesis, 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, independent of males, observed in Baphnia, 

 Ajms, and Limnadia. Ever since that period, Siebold has continually 

 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 

 was 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, while other 

 broods occur in which both sexes are present. The number of Apus 

 of two species — Apus cancriformis and Apus productus — 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 

 iu)mense quantities), and had the opportunity of studying 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 several hundreds of the Apus 

 from the pond, he. never found a single male among them. On one 

 occasion, he had the whole contents of the little pond removed with the 

 greatest care, so as to feel sure that he had obtained every Apus present. 

 He obtained on this occasion 5,796 specimens of Apus, every one of which, 

 ieing carefully examined, proved to be a female. At the same time, 2,576 

 specimens of BrancMpus were obtained from the pond, which were, as 

 usual, of both sexes. In those cases where ponds afforded both males 

 and females of Ajms, it is remarkable that the proportion of the sexes 

 was very variable. The highest proportion of males appears to be in 

 a case recorded by Sir John Lubbock, who found 33 male and 39 

 female Apus productus in a jjond near Kouen ; while among 193 

 specimens of Apus cancriformis, from a locality near Krakou, only one 

 male occurred. What is most important about this variation in the 

 proportion of males to females is that in two or three localities, furnish- 

 ing mixed generations of Apus, from which he has received, year alter 

 year, numbers of specimens, Siebold has observed an apparent con- 

 stantly augmenting disproportion of males to females, and ho is led 

 to the supposition that, in these cases, the males will at last cease 

 altogether, and thus a female generation be produced, which will con- 

 tinue to reproduce itself parthenogenetically, as in the Gossberg and a 



