A TABLE FOE STUDENTS 313 



According to the table the family can always be as- 

 certained by the external characters, except in the case 

 of the females of the Vaunthompsoniidse and Leiiconidae, 

 and there the eye is generally available, since it is absent 

 from all the Leuconid^, and indistinct only in one genus, 

 L&ptocuma, of the Vaunthompsoniidse. The Campy laspid as, 

 which in the table are but slightly distinguished from the 

 Nannastacidse, are strongly distinguished externally both 

 from them and all other Cumacea by the backward bulging 

 carapace, as also by the stiliform molar process of the 

 mandibles and internally by the single pair of liver 

 tubes. 



The genealogical relationships of the Cumacea are ob- 

 scure. The second antennas of the male resemble what is 

 often seen in the Amphipoda. The epipod of the first 

 maxiilipeds helps the respiration, as in the Mysidas and 

 cheliferous Isopods, but with the important addition of 

 sessile branchial sacs. In the swimming branches on 

 some of the perasopods there is a weighty resemblance to 

 the Mysidse. The mouth-organs make some approaches 

 to those of the Isopoda, and, as with them, the young are 

 hatched before the development of the last pair of pereeo- 

 pods. The pleon recalls the paleeozoic Phyllocarida and 

 their existing representative Nebalia. 



It will have been seen by the number of genera and 

 species to which the name of G. 0. Sars is attached that 

 he has made a special study of this sub-order, and this 

 sketch of it is deeply indebted to his numerous and lumi- 

 nous works upon the subject, to which, indeed, must be 

 credited the clearness and accuracy with which this small 

 but very interesting group is now known. 



