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-hke enlarge- 





Fig. 23 



A. Transverse section across the thorax of A/us cancrifonnh^ semi- 

 diagrammatic, cs, cephalic shield ; ht, heart ; pc^ pericardial cavity ; 

 int^ intestine ; go, gonads, lying in the perivisceral sinus ; «<:, nerve cord ; 

 hr, bract ; ^, fiabellum ; gn^ gnathobase ; en^, en'^^ second and third 

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

 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 ; ai, first antennary nerve ; a"^^ second 

 antennary nerve \sg'^, first stomatogas trie nerve \sg'^, second stomatogastric 

 nerve; vid^ mandibular nerve ; ■jnx'^, first maxillary nerve; w-r^, second 

 maxillary nerve ; /Ai, 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 



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