/. CRUSTACEA: LEPTOSTRACA. 427 



Legion I. Leptostraca. 



The Leptostraca connect the Phyllopoda with the higher 

 groups. They have twenty-one somites, eight abdominal, eight 

 thoracic, and five cephalic, and this and the openings of the genital 

 ducts ally them to the Malacostraca. On the other hand the 

 bivalve carapace covering the cephalothorax and part of the abdo- 

 men, and the leaf-like thoracic feet, are phyllopodan. They have 

 an antennal gland and a rudimentary shell gland ; an elongate heart 

 which extends through cephalothorax and abdomen; and com- 



Fie. 432. Nebalia Znpes.* (After Sars.) 7t, heart; i, intestine; o, ovary; a, adductor 

 of carapace ; b, brain ; r, rostrum. 



pound stalked eyes. The few species are all marine and belong to 

 the genus Nebalia. N. Mpes * (fig. 432). 



Legion II. Thoracostraca (Podophthalmia). 



The names given this division have reference, first, to the fact 

 that the head and more or fewer of the thoracic segments are united 

 into an immovable part, covered by a firm carapace; second, that 

 the compound eyes (except in Cumacea) are placed at the ends of 

 movable eye stalks, a condition which has possibly arisen from 

 the inflexibility of the anterior part of the body. The first five 

 appendages are always two pairs of antennae, a pair of mandibles, 

 and two pairs of maxillae. The remaining pairs vary greatly in 

 character and from one to three may be modified into maxillipeds, 

 while the abdominal somites except the last (telson) usually bear 

 appendages, at least in the female. There is usually a metamor- 

 phosis in development in which a nauplius-stage may appear, most 

 frequently in the lower forms (schizopods), but even in the deca- 

 pods (Peneus). 



