306 Mr. H. M. Bernard on 



In this latter case the transformation takes place in the 

 same individuals, parthenogenetic females becoming sexual 

 females. Where do the males, which this rapid transforma- 

 tion in the females implies, come from ? Kurz speaks of the 

 interval of time which must necessarily elapse before any of 

 the young can develop into males, and during such an interval, 

 he suggests, hermaphroditism may occur. Are these herma- 

 phrodites transformed parthenogenetic females, as the herme- 

 phrodite Apodidae appear to be ? If so, is it absolutely 

 necessary to suppose that they stop at hermaphroditism? 



With regard to the Apodidas, the records of " finds " do 

 not show that the males begin to appear in the fall of the 

 year. The rain-pools in which Apus lives are most likely to 

 dry up and render life difficult in midsummer. Hence males 

 may occur at any time of the year, whenever, in fact, the 

 rain-pools threaten to dry up ; that is, if the law is the same 

 for Apus as for Cladocera — that males appear when the 

 conditions of life are unfavourable. 



If this be the case, where do these much-needed males of 

 Apus come from ? Do they develop from eggs specially laid 

 under the influence of .the adverse conditions, or do a certain 

 number of developing young ones become males instead of 

 becoming parthenogenetic females, as, under favourable cir- 

 cumstances, would have been the case ? These are questions 

 which cannot be finally answered for want of data. A few 

 points, however, are worth considering. 



Claus * found that a developing Apus cancriformis at the 

 twelfth ecdysis showed clear signs of the transformation of 

 the eleventh leg into the egg-pouch, but that at this stage its 

 dorsal shield measured only 2^ millim. — that is, the animal 

 was still very small. How long it took to grow to this size 

 is apparently not stated. Brauer f found that Lepidurus 

 2?roductus was 7 millim. long after the seventh ecdysis and 

 sexually mature after the twelfth, which took place thirty- 

 seven days after hatching. Here are certainly remarkable 

 differences between the courses of development in these two 

 forms, but they appear to agree in showing that the process 

 is a slow one. It appears certain, then, that males could not 

 be produced from eggs for an emergency. It would take too 

 long. The eggs laid when the pools were in process of drying 

 up would certainly take more than a month to hatch out and 

 develop into sexually mature animals. Indeed, the assumed 

 unfavourable conditions under which they would be growing 

 would still further retard their development. It seems more 

 * Abb. k. Ges. Wiss. Gottingen, Phys. Class, xviii. (1873). 

 t SB. Akad. Wiss. Wien, Bd. lxix. Abtb. i. 1874, p. 130. 



