SEA-FISHERIES LABORATORY. 375 



" The system of blood-containing spaces pervading the 

 body in Mollusca and Arthropoda is not, as sometimes 

 supposed, equivalent to the coelom or perivisceral space of 

 such animals as the Chaetopoda and the Vertebrata, but 

 is in reality a distended and irregularly swollen vascular 

 system — the equivalent of the blood-vascular system of 

 Chaetopoda and Vertebrata.''* 



In Cancer the only remnants of the true coelom are 

 the gonadial sacs and the end sacs of the antennary 

 glands. The labyrinth and bladder of the excretory 

 system are lined by cells derived from epiblast. 



ALIMENTARY CANAL 



(Pis. V, VI, VII). 



The alimentary canal extends from the mouth, which 

 is situated on the ventral side of the cephalic region 

 between the mandibles, to the anus on the ventral side 

 of the telson. The nature of the development of the 

 alimentary canal suggests a natural division into three 

 parts: — (1) The fore-gut, which is the embryonic 

 stomodaeum, (2) the mid-gut, the archenteron of the 

 embryo, and (3) the Kind-gut, which is the embryonic 

 proctodaeum. 



Fore-gut. 



The fore-gut commences at the mouth and is formed 

 of the embryonic epiblast. It is lined throughout by a 

 cuticle which is continuous with the exoskeleton around 

 the mouth. The mouth leads into a short oesophagus 

 (PL VI, fig. 40, oe.) which opens into the so-called 

 " stomach," which is continuous behind with the mid-gut. 



The mouth is situated on the ventral surface of the 



* Lanke&ter, E. Ray. " The Enterocoela and the Coelomocoela," 

 A Treatise on Zoology, Part II. 



