SEA-FISHERIES LABORATORY. 321 



on itself longitudinally to form a tube. This distal 

 portion probably represents the endopodite (end.). The 

 two basal portions fuse in the middle line, thus forming 

 a tunnel-like structure extending backward below the 

 second somite. Below the fused basal portions of the first 

 pleopods arise the second pair of appendages (PI. II, 

 fig. 15). Each consists of two parts — a horizontal rod 

 (prot.) projecting posteriorly, and a vertical rod (end.) 

 attached to the posterior end of the first portion. The 

 vertical rod is divided into two parts by a transverse 

 groove. The horizontal rod probably represents the 

 protopodite, and the vertical portion is the endopodite. 

 There is no trace of an exopodite on any of the male 

 pleopods. 



The vertical rod-like portion of the second pleopod fits 

 into the tube of the first pleopod. 



ENDOPHKAGMAL SKELETON 

 (PL III, fig. 18, Text figs. 4, 5, 6, 7). 



The post-oral region of the cephalothorax has an 

 extremely complex system of internal plates, known 

 as the endophragmal skeleton. Essentially 

 this system may be said to consist of a number of 

 inwardly-projecting plates arranged transversely so as to 

 divide up the interior of the cephalothorax into a 

 series of irregular compartments. Each partition, or 

 arthrophragm, arises at the junction of two somites, 

 and is formed by an infolding of the sternal and epimeral 

 exoskeleton between these somites. Thus, each plate of 

 the endophragmal skeleton is double, and is composed of 

 two flattened plates of exoskeleton which are closely 

 applied together. 



The primary function of the endophragmal system is 



