308 THE ANATOMY OF INVERTEBRATED ANIMALS. 



The Glass-crabs, or Phyllosomata (Fig. 80), are singular 

 marine pelagic Crustacea, in which the body consists almost 

 wholly of two large, extremely flat and transparent disks, 

 devoid of any segmentation. The anterior of these bears 

 the pedunculated eyes, the antennules and the antennae on 

 its anterior margin ; while the labrum, with the mandibles 

 and anterior pair of maxilla?, form a small projection poste- 

 riorly on its ventral surface. The second pair of maxillae is 

 situated a little more backward and outward, and bears a 

 scaphognathite ; and just behind these appendages is the 

 fold of a cervical groove which separates the anterior disk 

 from the posterior. The anterior disk contains the stomach 

 and the liver, and in this respect, as in its appendages, cor- 

 responds exactly with the cephalostegite of the carapace of 

 an ordinary Crustacean, and its six cephalic sterna. The pos- 

 terior disk, on the other hand, contains the short and almost 

 round heart, with the intestine, and bears the eight pairs of 

 thoracic appendages, the anterior and posterior of which are 

 not uncommonly rudimentary. The abdomen is usually very 

 small, and situated in a notch at the posterior edge of the 

 thoracic disk. It is provided with six pairs of appendages. 

 No generative organs have been found in the Phyllosomata., 

 and there is reason to believe that they are merely larvae of 

 the Macruran genera Pallnurus, Scyllariis^ Thenus^ and their 

 allies. 



The Cumacea. — These are very remarkable forms, allied to 

 the Schizopoda and JVehalia^ on the one hand, and on the 

 other to the Edriophthalnvia and Copejjoda ; while they ap- 

 pear, in many respects, to represent persistent larvje of the 

 higher Crustacea. 



Cuma Rathkii might, at first, be readily mistaken for a 

 Copepod. It possesses a comparatively small, thick carapace, 

 apparently produced into a rostrum anteriorly, and succeeded 

 by a series of twelve gradually narrowing free segments, the 

 appendages of which are in great part obsolete. The last of 

 these segments is a pointed telson ; the anterior five, belong- 

 ing to the thorax, bear thoracic limbs, while the eleventh, the 

 last true somite of the body, carries its characteristic styli- 

 form appendages. The appendages of the preceding abdom- 

 inal somites may be either absent or very small and rudimen- 

 tary. Dohrn has proved that this is true only of the females 

 among the Cumacea. The males, which were formerly re- 

 ferred to the genera Bodotria and Alauna^ often have well- 



