38 



ATURAL HISTORY OF ARTHROPODS. 



a temperature of 60 to 65, but at 85 the nauplii appear in less than twenty-four hours. 



This power of withstanding the effects of dessication has enabled naturalists to 



study the habits and development of these 

 interesting Crustacea in places far from their 

 original habitat. Thus Professor Glaus, in 

 Vienna, found it easy to investigate the an- 

 atomy of Daphnia atkinsoni, from Jerusa- 

 lem ; Professor Siebold, at Munich, was en- 

 abled to study the habits of Artemia gracilis, 

 hatched from mud brought from Great Salt 

 Lake ; and Dr. Gissler, in Brooklyn, studied 

 the embryology of Apus lucusanus, from eggs 

 obtained in the same manner from Kansas. 

 The figure we give of the nauplius of Apus 

 was drawn by Dr. Gissler from one of these 

 specimens. 



There are three well-marked families of 

 Anten- Phyllopoda, all of which are represented 

 in North America. The first family, LIMNI- 



FIG. 50 Nauplius of Apus lucasanus. a', 

 nulse. a". Antennae, m. Mandible. 



;, has the body enclosed in a bivalve shell, the antennulae small, the antennae 

 large and well developed ; from ten to twenty-seven pairs of swimming feet. In the 

 male one or two of the first pairs of feet are provided with a pincer, while in the 

 females they are simple. The telson is large, and bears a pair of appendages. The 

 genera are four in number, Limnetis, Estheria, and 

 Limnadia being the most prominent. Compared 

 with the other families the Limniadiadas possess but 

 few points of popular interest. 



The family APODID^E contains but two genera, 

 Apus and Lepidurus. In these the anterior portion 

 of the body is flattened, and covered with a broad 

 and somewhat ovate carapax, from beneath which 

 the abdominal segments project behind, giving the 

 animal, at the first glance, a somewhat striking re- 

 semblance to the horse-shoe or king-crab, .Limulus, 

 with which, indeed, they were originally classed by 

 Otto F. Mttller. As in the preceding family, the 

 compound eyes are sessile. The antennae are small, 

 the second pair sometimes being absent ; the post- 

 oral appendages usually number sixty-three pairs, 

 some of the segments bearing as many as six pairs 

 apiece. The eleventh pair are modified to form the 

 egg-sacs in the female. The terminal segment of 

 the body bears two long-jointed appendages, and ter- 

 minates either abruptly (Apus) or in a long paddle- 

 like outgrowth (Lepidurus). The family has its best 

 representation on our western plains and in the Rocky Mountains, where six species 

 occur, while from all the rest of the world less than twenty species are known. In 

 America, outside these limits, but three forms are known, one in Greenland, one in 



FIG. 51. Apus cequalis, natural size. 



