PHRONIMA. 



3246 THE JOINTED ANIMALS 



thorax is cylindrical, and the abdomen, with its limbs, rudimentary. In the typical 

 Caprella the third and fourth thoracic segments are without legs, but bear a pair of 

 branchial vesicles; the appendages of the second pair are developed into claspers, 

 and those of the last three pairs are of the ambulatory type. These shrimps seldom 



swim, but climb among the branches of seaweeds and 

 zoophytes. When at rest, they grasp the stems of the 

 weeds with their hind-limbs, and, holding the body in 

 an erect position, wave their long antennae in search 

 of prey. In the whale lice, which live parasitically 

 upon cetaceans, the short and conical head is united 

 to the first segment of the thorax, which consists of 

 six free, flattened segments. As in Caprella, the third 

 and fourth segments of the body bear no limbs, but 



(Enlargld three "times.) are furnished with a pair of gills, usually turned over 



the animal's back. In the female these segments 



carry beneath them plates, forming sacs, for the eggs. The second, fifth, sixth, 

 and seventh segments are provided with short limbs, terminating in a sharp, pointed 

 segment, which closes against the enlarged penultimate segment as the blade of a 

 pocket-knife closes on its handle. By means of these chelate appendages the 

 animals fasten themselves to the skin of cetaceans, thrusting their sharp claws 

 into the epidermis, and adhering so firmly as to be able to withstand the dash of 

 the waves. 



The members of the tribe Hyperina differ from the last by the larger size of the 

 head, the more prominent eyes, and the absence of a palp on the maxillipedes. 

 To this tribe belongs the large Cystosoma, a pelagic animal, probably retiring during 

 the day to a considerable depth, but occasionally coming to the surface. The animal 

 is colorless and transparent, so that by transmitted light the internal organs can be 

 seen. The head is large and inflated, with its upper surface occupied by two enor- 

 mous eyes. The genus Phronima also contains species attaining a considerable 

 size, examples of the European P. sedentaria exceeding an inch in length. As in 

 Cystosoma, the second pair of antennae are obsolete; the head is large, with the 

 eyes placed upon its summit. There are seven pairs of large thoracic appendages, 

 the third from the end forming a large and strong pincer. 



The species are widely distributed, although most abundant in the Tropics. 

 l,ike many pelagic animals, they are translucent, and mostly live in the mantle 

 cavity of the ascidians Pyrosoma and Doliolum, where the eggs are laid, and the 

 young hatched. 



To a certain extent connecting the Malacostraca with the Kntomostraca is a 

 group of Crustaceans known as the Leptostraca, and containing the three recent 

 genera Nebalia, Nebaliopsis, and Paranebalia, and a number of fossil forms. The 

 affinities of the group seem to lie with the Phyllopods on the one hand, and the 

 Schizopods on the other. The body is laterally compressed, and the whole of 

 the cephalothorax and the first four segments of the abdomen enveloped in a cara- 

 pace, which springs from the head, and is formed of two movable valves, closed by 

 a muscle. Although the eight thoracic segments are overlapped by the carapace,. 



