664 



FRESH-WATER BIOLOGY 



Fig. 1013. Estheria morsei, with left valve of shell removed. X 9- 

 ai, first antenna; 02, second antenna; c. carapace; d, cercopods 

 or furcal rami; /, flabella; u, umbone. (After Packard.) 



The alimentary canal of phyllopods consists of a large mastica- 

 tory and glandular atrium produced by an overhanging labrum 



c in front of the mouth; 



this is followed by a 

 buccal cavity, a ver- 

 tical esophagus and a 

 small globular stom- 

 ach within the head; 

 and, behind these, is a 

 long straight intestine 

 which terminates in a 

 short rectum at the 

 posterior end of the 

 body. The heart is 

 greatly elongated in 

 the Anostraca, oc- 

 cupying nearly all the trunk-somites, with a pair of ostia opening 

 in each somite. In the Notostraca and Conchostraca it is more 

 restricted — and extends through only three or four segments in 

 the latter. There are no definite blood vessels. A maxillary gland 

 (consisting of an end-sac, glandular coiled tube, and short terminal 

 duct) serves as an excretory organ in phyllopods. The ladder-like 

 structure of the ventral nerve chain shows the primitive character 

 of the nervous system. 



After leaving the egg, all American 

 phyllopods begin their development as a 

 free swimming nauphus or metanaupHus 

 (Fig. 1014). Some differences exist even 

 in closely allied forms in regard to the 

 stage ot development reached at hatching. 

 The larvae of the Notostraca and Anos- ^'f;iformis, ^sfh^Sd!^ ^MtRiaus, 



, , 1 • .. J.1 i.* from Lankester's Treatise on Zoology.) 



traca are typical metanauplei at the time 



of hatching, with an oval body that shows the beginning of several 

 trunk-somites posteriorly and sometimes the rudiments of their 

 appendages. The first antennae are well developed but uniramous, 

 the second antennae have a movable masticatory process and the 

 mandibles are but feebly developed. The earliest conchostracan 



