ENTOMOSTRACA. 



39 



the West Indies, and the third in Lower California. None are known in the United 

 States east of the Mississippi River. The Apodidse frequent shallow pools, where 

 they sometimes occur in countless myriads, swimming, like 

 the members of the next family, upon their backs, with a 

 graceful motion, or burrowing in the soft ooze of the bot- 

 toms of the puddles, somewhat like a Ziiniulus, in search of 

 food, which, so far as is known, is of an animal nature. 



The most interesting feature in connection with Apus is 

 its parthenogenetic reproduction, which also occurs in JLepi- 

 dicrus, Limjiadia, and Artemia among the Phyllopoda, as 

 well as elsewhere in the Arthropoda. In plain English, par- 

 thenogenesis means a reproduction by means of unfertilized 

 eggs, the influence of the male element being unnecessary. 

 The investigations of this interesting subject are mainly the 

 work of Professor Siebold, of Munich. He was led to study 

 by the fact that at that time (1856) no males of Apus cancri- 

 formis were known. In 1858 males were discovered, "and 

 Siebold received specimens from various localities. He thus 

 learned to distinguish with perfect facility the two sexes, and 



was able to convince himself that with Apus broods occur which are entirely desti- 

 tute of males, and go on reproducing parthenogenetically, while other broods occur 

 in which both sexes are present." "On one occasion, he had the whole contents 

 of a 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 

 Ajnis, every one of which, being carefully examined, proved to be a female." After- 

 ward he experimented with Artemia, using every care to exclude males and sperma- 

 tozoa, and demonstrated beyond a question that virgin females will deposit eggs 

 from which, unfertilized by any male sperm, a brood can develop. How far either 

 Apies or Artemia can continue reproducing parthenogenetically has not yet been 

 determined. 



The Beanchipodid^, the highest family of the order, lacks the carapax, so char- 

 acteristic of the other two, though the homologues of the shell glands persist in a rudi- 



FiGS. 52. — Dorsal and side 

 views of Lepidurus couesiif 

 natural size. 



Fig. 53. -BrancMnecta colomdensis. a. Male. l. Female, u. Front of head of male, showing claspers. 



mentary condition in the adults of at least some species. The head is small, and the 

 compound eyes are placed upon a stalk similar to that in the Podophthalmia (to be 

 discussed further on), while the median ocellus (the eye of the nauplius) persists in 



