160 Transaction.?. — Zoology, 



is composed appear to be modifications of the naked jointed seta? already 

 described. There is a joint about the middle (pi. XXI., fig. 4 a). The 

 basal part is quite naked, the distal half is naked until some little distance 

 past the joint, but is then thickly covered with short simple filaments. 

 Tbese filaments extend nearly to the end of the seta, which is hooked (b). 

 In the concave portion of the hook there is often a slight projection (c). 



The iimer surface of each branchiostegite is thickly covered with jointed 

 seta?. In tbese the filaments on the distal half are less conspicuous than 

 in the coxopoditic seta? ; in this point they are intermediate between the 

 coxopoditic seta? and the ordinary jointed seta? found on the chela?, etc., but 

 they resemble the coxopoditic seta? in having their extremities hooked. On 

 the inferior edge of the branchiostegite there is a row of seta? hanging 

 downwards. These are similar to those found on the inner surface of the 

 branchiostegite except that the extremities are not hooked. I am quite 

 ignorant of the function of all the hooked seta? that I have described ; they 

 appear to have sometbing to do with the respiratory organs, as it is only 

 those in immediate connection with the respiratory organs that are hooked. 



Circulatory system. — The circulatory system, as far as could be seen 

 without injection, does not appear to differ in any important particular 

 from that of Astacus. The heart is of similar shape and lies behind the 

 stomach and above the intestine and reproductive organs. The abdominal 

 artery was readily seen running along the dorsal surface of the abdomen 

 and giviug off branches in each somite. The sternal artery was also seen 

 passing vertically downwards to tbe ventral surface of the animal, where it 

 divides into an anterior and a posterior branch. The arteries arising from 

 the anterior portion of the heart are smaller and are not so readily seen. 



Alimentary system. — The general course of the alimentary canal is, as 

 might have been expected, very much like that of Astacus. The oesophagus 

 is large in section and expands almost immediately into the capacious 

 stomach. The stomach consists of two parts, the cardiac and the pyloric, 

 the former of which contains a gastric armature, which is fully as compli- 

 cated as that of Astacus. It is formed on the same type, so that the same 

 names can be used in describing the various parts. The anterior edge of 

 the cardiac ossicle (pi. XX., figs. 5 and 6 c) is much more convex than in 

 Astacus ; and the remaining part is divided into four portions, as shown in 

 fig. 5. The urocardiac process (uc) is more or less oblong, not quite twice 

 as long as broad, with the sides slightly concave, at the posterior end are 

 two rounded prominences. The median tooth (mt) is dense and hard ; the 

 end curves forwards and is bifurcated at the summit. The urocardiac 

 process and the median tooth are united by tbe prepyloric ossicle (pp) to 

 the pyloric ossicle (p) in the same way as in Astacus. The pterocardiac 



