THE ARTHROPODA 



103 



its subsequent course is not accurately known, but it probably 

 is returned to the head, and joins the stream flowing back- 

 wards through the perivisceral sinus. 



The excretory organs of Apus are the shell-glands already 

 mentioned. Each gland consists of a coiled tube divisible 

 into the following parts : (i) Distally a bladder-like enlarge- 



Fig. 23 



A. Transverse section across the t'horax of Apus cancriformis, semi- 

 diagrammatic, cs, cephalic shield ; /if, heart ; pc, pericardial cavity ; 

 int, intestine ; go, gonads, lying in the perivisceral sinus ; nc, nerve cord ; 

 br, bract ; _/7, flabellum ; gn, gnathobase ; en^, en^, second and third 

 endites of the limb. B. The shell-gland of Apus, after Bernard. /, 

 excretory aperture ; bl, bladder ; es, end-sac ; V, second maxilliped. C. 

 Anterior part of the nervous system of Apus, after Zaddach and Pelseneer. 

 Syn, syncerebrum; op, optic nerve; a*, first antennary nerve ; a*, second 

 antennary nerve ; jg-i , first stomatogastric nerve \s^, second stomatogastric 

 nerve; md, mandibular nerve ; w_ri, first maxillary nerve; mxi^ second 

 maxillary nerve ; th^- , nerve to first thoracic limb. 



ment lying in the bract of the second maxilla. This bladder 

 is lined by a chitinised membrane, and is produced externally 

 into a short canal which opens at the extremity of the 



