562 



Dr. W. C. Mcintosh on 



[Feb. 22, 



vessel, which proceeds backward, collecting, as it goes, the capillary 

 streams, and then ends by turning forward at the base of the snout as 

 the efferent cephalic vessel. The latter has no evident capillaries, but 

 bends round at the tip of the flattened organ to terminate in the alferent 

 cephalic vessel. A curious change takes place in the majority of those 

 Magelonce which are pro\dded with the convoluted lateral organs 

 of the body, mentioned further on, in autumn. The cephalic vessels 

 are much abbreviated, and the direction of the current at the base of the 

 snout is somewhat modified. The blood from the head and anterior 

 region collects into a series of large vascular meshes which occur in the 

 anterior region of the body, and in which the current is for the most part 

 under the control of the greatly developed muscles of the body-wall. 

 Thus it happens, as formerly indicated, that the contraction of the latter, 

 and of the special muscular apparatus which closes the communication 

 with the posterior region at the ninth segment, drives the blood forward 

 to unroll the proboscis. This muscular arrangement in the anterior region 

 and the muscular walls of the vessels themselves at the posterior part of 

 the same division of the body send the current through the relaxed barrier 

 at the ninth segment into the muscular ventral blood-vessel of the pos- 

 terior region, and onward to the tail, where the trunk ends by bifurcating 

 into the two dorsal vessels. In each segment a lateral branch leaves the 

 ventral trunk at the anterior dissepiment, turns round and proceeds back- 

 ward to the next dissepiment, and terminates in the branch to the dorsal 

 vessel. Further, as first observed by Dr. Fritz Miiller, a sac-like dilatation 

 takes place shortly after the commencement of the latter, and it fills at 

 intervals, the distention being followed by a contraction which sends the 

 blood onward by the branch to the dorsal vessel. 



In vigorous specimens, the currents of the blood are as swift and 

 beautiful as in the tails of young salmon and other translucent verte- 

 brates. When examined in the liquor sanguinis of the living animal (as 

 in a favourable view of a healthy tentacle) the blood-corpuscles show a 

 pale nucleus. 



Nervous System. — The central mass of the nervous system lies in front 

 of the preoral chamber in the fork of the median muscles, and consists 

 of the ordinary ganglion-cells with connective-tissue bands. ISTo eyes 

 or other sense-organs exist, though the animal is extremely sensitive to 

 light and other stimuli, and lives in regions where there is abundance of 

 sunshine. Two main nerve-trunks proceed backward in the hypoderm — at 

 first outside, then under, and finally to the inner border of the ventral 

 longitudinal muscles. At the commencement each is accompanied by a 

 neural canal (the " tubular fibre " of the late M. Claparede) ; but, before 

 leaving the anterior region of the body, 'the canals glide inward and 

 coalesce into a single large median one. The whole central nervous 

 system is hypodermic. 



So far as present examination goes, the Annelida present four con- 



