SEA-FISHERIES LABORATORY. 439 



stain will pass out into the lumen of the tubule and thence 

 to the alimentary canal, where it is got rid of along with 

 the excrement. 



(iii) Branchial Excretory Organ. 



This is found in the gills in that portion of the tissue 

 situated between the afferent and efferent branchial veins. 

 According to Cuenot, the excretory cells are continued 

 along the sides of the branchio-cardiac veins When the 

 crab is subject to Cuenot's system of injection, it is found 

 that the cells of the branchial excretory organ act like 

 the cells of the end sac They have an acid reaction and 

 eliminate substances of the second category. 



NERVOUS SYSTEM. 



The nervous system of the Brachyura {Carcinus 

 maenas) has been investigated in detail by Bethe.* It is 

 proposed to give here only a short account of the nervous 

 system of Cancer. 



The nervous system may be described briefly as 

 consisting of two main nerve masses — the fused pre-oral 

 cerebral ganglia and the fused ganglia of the post-oral 

 region. The two are connected by a pair of commissures 

 which pass round the oesophagus. With the cerebral 

 ganglia are connected the nerves supplying the eye, 

 antennules and antennae. All the post-oral appendages 

 and somites are innervated from the posterior nerve mass 

 which lies in the thorax. At each side of the oesophagus 

 there is a ganglion on the commissure, from which arises 

 the stomatogastric nerves supplying the fore-gut. 



The brain is the centre of co-ordinated movement, 



and each ganglion of the ventral nerve mass is the reflex 



centre for the appendage which it supplies. 



* Bethe. Arch. f. Mikr. Anat., Bel. XLIV (1895), pp. 579-622; 

 Bd. L (1897), pp. 160-546, 589-639 ; Bd. LI (1898), pp. 382-152. 



