66 



free surface of the gland, and in cross section appear as 

 narrow passages. From these passages secondary canals 

 run into the substance of the gland, and end in rounded 

 chambers. Into these chambers open minute caeca, 

 whose walls consist of the glandular excretory cells of the 

 organ. All the above passages are lined with non- 

 glandular cells. Blood entering the branchial heart, 

 tills the passages excavated in its Avails, some of which 

 extend into the substance of the adjacent pericardia] 

 gland. The blood thus comes into contact with the 

 excretory cells of the branchial heart appendage, and is 

 there deprived of waste matter. 



A ElfVOLS SYSTEM. 



All Cephalopods have a highly concentrated nervous 

 system, which reaches its maximum in Argonauta, 

 Octopus and th.&n^Eledone ranking next in the series. 

 The typical aiolluscan ganglia are so closely approxi- 

 mated, and so intimately connected, as to form a 

 peri-oesophageal nerve collar, just behind the buccal mass, 

 and between the eyes (PL IX, figs. 70 and 76). In 

 Eledone, this collar or " brain " is enclosed in a tubular 

 cartilaginous capsule, the anterior and posterior ends of 

 which are closed by tough membra nes. These are 

 pierced for the passage of the oesophagus, posterior 

 salivary duct, pharyngeal arteries, &c. (PI. X, tigs. So,/ 

 and b, and 82, P.M.). Round the brain, and separating 

 it from the cranial walls, is found a kind of gelatinous 

 transparent tissue. - 



Four pairs of ganglia, the cerebral, the brachial, the 

 pedal, and the visceral ganglia, form the brain of Eledone. 

 These pairs of ganglia are, however, very intimately 

 fused together, and although the supra-oesophageal or 



