LOBSTERS, CRAYFISH, ETC 



271 



family, Sergestidce, in which the gills are impoverished or lost, while the first 



pair of trunk-legs and sometimes the second are simple, the chelae of the third are 



minute, and the fourth and fifth pairs 



are feeble, rudimentary, or absent. To 



this family belongs the genus Leucifer, 



remarkable for having the eyes and 



antennae supported at the end of a long 



neck which extends in advance of the 



mouth. The gills are absent, respiration 



being effected by means of the general 



integument, which is so thin that the 



internal organs can be seen. In the 



figure the dark line (n) is the ventral 



nerve - chord which throws out finer 



branches from ganglionic swellings in 



each of the segments ; (h) is the heart, 



while immediately below the latter is 



the stomach, passing forwards into the 



gullet and backwards into the intestine. 



Cleft-Footed Group,- 

 Schizopoda. 



-Order 



This name is applied to a group 

 nearly allied to the long-tailed Decapods ; 

 the chief difference between them being 

 in the fact that in the present order the 

 eight thoracic limbs are similar in struc- 

 ture, each being pecliform and provided 

 with a distinct exopodite on the second 

 segment. The gills, which are attached 

 either to the thoracic or abdominal 

 appendages, generally project into the 

 water, and are but rarely concealed in a 

 chamber. The eggs are carried by the 

 female beneath the trunk, and are fre- 

 quently protected by the development of 

 a pouch. The order contains several 

 families embracing a large number of 

 mostly marine forms, some of which occur 

 at great depths. Of the British species, 

 the finest is Nyctiphanes norvegica, which 

 forms an important part of the food of 

 herrings. It has luminous organs on the 

 thorax and abdomen, and when swimming in a glass vessel, in a darkened room, 

 appears like a flash of light. The young, as in all the members of the family 



long-necked shrimp, Leucifer (much enlarged). 



