1885.] NEW ZEALAND EARTHWORMS. 821 



sinus in the walls of tlie intestine itself; but I have little doubt, from 

 the analogy oi Acanthodrilus novce zelandicB, that such a sinus exists. 

 A delicate layer of transverse muscles, continued into the typhlosole 

 from the intestinal walls, enclosed the blood-plexus. 



§ Vascular System. 



Concerning the vascular system of Acanthodrilus I have but few 

 remarks to offer ; to study the circulation thoroughly it is requisite 

 to have living specimens. 



In a short paper in the ' Proceedings of the Royal Physical 

 Society ' ' I have referred to the double condition of the dorsal vessel 

 in two of these species, so that I need do no more than briefly reca- 

 pitulate the main points of that paper, which are as follows : — In 

 the genera Megascolex and Microchceta the anterior section of the 

 dorsal vessel is formed of two separate tubes, which become united 

 at the points where they traverse the mesenteries. In AoanthodriJus 

 novce zelandicd the separation of the dorsal vessels into two distinct 

 tubes has gone a step further (PI. LIII. fig. 6) : the whole of the 

 vessel except the anterior extremity lying upon the pharynx is divided 

 into two separate tubes which only unite at each mesentery. In 

 A. dissimilis, which agrees so closely in external as well as in 

 anatomical characters with A. novce zelandicc, the dorsal vessel is a 

 single tube, and appears to be always so. It is not possible, how- 

 ever, to use this retention of an embryonic character in A. nova 

 zelandm, which is analogous to the partial retention of the left 

 aortic arch in the Raptores among birds, to distinguish the species 

 absolutely from A. dissimilis, for in one example of the former 

 species the dorsal vessel was single. 



In A. multiporus the primitive double condition of tlie dorsal 

 vessel is more comf)lete still. In this species the dorsal vessel is 

 composed of two tubes which run from end to end of the body and 

 are not fused at the mesenteries. 



The dorsal vessel is connected with the ventral (supra-ncrvian) by 

 a number of transverse trunks, the last pair of which are situated in 

 the thirteenth segment. The last four pairs arise both from the 

 dorsal and supra-intestinal trunks, as Perrier has recorded in Ponto- 

 drilus and other genera. 



The supra-intestinal trunk lies on the surface of the alimentary 

 canal, and is concerned with the supply of the intestinal blood-plexus. 

 In one specimen of A. novce zelandicB this vessel was double ; 

 beneath the CESophagus is another longitudinal blood-vessel, which I 

 did not observe in tlie intestinal region. 



The supra-nervian trunk is connected with the median ventral 

 line of the intestine by a mesentery ; and in the oesophageal region 

 the dorsal vessel, which here lies some way above the alimentary 

 tract, is connected with it, as elsewhere, by a similar mesentery, or 

 two, one for each dorsal vessel where it is double. 



In the thirteenth to about the nineteenth segment is a lateral 

 vessel on either side ; it appears to arise from a transverse heart. 



1 1884-85, p. 424. 



