616 GEOLOGICAL SURVEY OF THE TEEEITORIES. 



great number of otUer ponds. This is, however, by no means proved ; 

 and we have no idea at present as to how the males may make their 

 appearance again, or what are the conditions affecting their develop- 

 ment and extinction. It occurred to Siebold that an objection might be 

 urged against parthenogenesis in Apus, in that, although he examined 

 consecutive generations, and found them always female, he could not 

 be sure that males had not been i)reseut before he took his specimens, 

 and had not died and decomposed after having fertilized the females. 

 To meet such an objection, he first made himself thoroughly acquainted* 

 with the male generative organs and the spermatozoa, and secondly 

 with the ovaries and their development. He found the spermatozoa to 

 be motionless like those of other Crustacea, and he never succeeded in 

 detecting any of them in the female genitalia among the specimens 

 belonging to supposed female generations. But he equally failed to 

 find spermatozoa, or a receptacle for them, in the female genitalia of the 

 specimens of mixed generations, and therefore no conclusion could be 

 drawn from the observation. The structure and development of the 

 ovum, however, made this observation decisive, since it was found that 

 an egg-shell forms round the ovum in the uterus, and, in the absence of 

 a micropyle, fertilization, if it takes place at all, must be accomplished 

 before this shell is hardened. A further proof of another kind was 

 obtained by experiment. Having removed eggs from females which 

 certainly at the time contained no spermatozoa, Siebold placed them in 

 a small tank, and from these obtained Apus embryos. Others were 

 reared to maturity from eggs taken in the pond. 



The relative size of male and lemale is a question about which there 

 is some interest; differences which have been observed seem to depend 

 on the fact that Apus continues growing as long as the pond in which it 

 lives does not dry up. Aiid hence the eggs which hatch soonest give 

 the largest-sized progeny. In his tabular statements, Siebold gives 

 measurements of the specimens examined by him at different times from 

 various localities. 



As to the other crustaceans named, which are Artemia salina and 

 Limnadia Hermanni, the occurrence of parthenogenetic broods is infer- 

 red from the descriptions of other writers whose works are criticised at 

 some length, and also from examination of specimens. It seems not 

 impossible, from an observation of Zenker, that in Artemia salina par- 

 thenogenetiic alternate with digenetic broods. In the beginning of the 

 year IbSl, this observer found th ee males among one hundred females; 

 later, in July, the same pond furnished thousands of females, but not one 

 male. 



It seems that males and females in this country have occurred in 

 Apus longicaudatus and Apus Lucasanus, but the males occurred in a 

 lot of A. wqualis from Kansas. It would appear as if the males from 

 Kansas must be those of A. cequalis; but they were undistinguishable in 

 form from A. Lucasanus from Cape Saint Lucus. Further observations 

 are needed to clear up the matter. More material from' the Western 

 States is greatly needed; and as much has been already contributed 

 by Dr. Hay den, it is to be hoped thiit the surveying parties sent out 

 under his direction may collect largely of them. 



This leads to the subject of the geographical distribution of the fresh- 

 water phyllopods of isforth America. Thus far no species of Apus has 

 been found in the United States east of the Mississippi nor in British 

 America. In Greenland and Arctic America, the Lepidurus glacialis 

 occurs. In the West Indies, Apus Bomingensis occurs at San Domingo. 



