426 Proceedings of the Royal Physical Society. 



trunks in being widely separated ; in Eunice and Mageloim 

 the two halves of the nerve cord as well as the two dorsal 

 vessels are close together. 



The fact of the development of the dorsal vessel of Crio- 

 drihcs and Lumhricus from two tubes gains additional signi- 

 ficance from a comparison with other groups of the animal 

 kingdom. Glaus has recorded that the heart of Apns arises 

 from two lateral rudiments; and in Geophilus Metchnikoff^ 

 has stated that the heart originates in a similar fashion; there 

 can be but little doubt that the heart in the Arthropoda, 

 together with its anterior and posterior aorta, is equivalent 

 to the dorsal trunk of the vascular system of worms. With- 

 out giving a complete list of those Arthropoda in which the 

 heart has a similar origin, it is worth while to refer to an 

 account by Dr Jaworovsky ^ of the development of the heart 

 in Chironomus ; in this insect the heart appears to arise from 

 two separate rudiments, which finally coalesce, but retain a 

 remarkable physiological independence, the one from the 

 other, which expresses the morphological distinctness of the 

 two sides of the heart ; the contraction of the heart has been 

 shown by Jaworovsky to be carried out independently of 

 each other by each of its two sides, so that although the 

 organ is in the adult only a single cavity, it bears unmis- 

 takable traces of having originated from a paired vessel; 

 such a physiological demonstration of a morphological fact 

 is of the highest interest. If the old idea of Geoffrey St 

 Hilaire that the " ventral " surface of an Annelid is homo- 

 logous with the "dorsal" surface of a vertebrate, be confirmed 

 by future researches — and there is at present evidently a great 

 deal to be said in favour of this view — then there is at least 

 some reason for supposing that the heart of the vertebrate 

 has been developed out of the dorsal vessel of its Annelid 

 ancestor ; in any case the relation of both to the intestine 

 would be the same, and the transverse trunks which connect 

 the dorsal with the ventral blood vessel in an Annelid have 

 an obvious resemblance to the aortic arches of a vertebrate ; 

 moreover, we know that the earliest rudiment of the heart 



1 Zeitsclir. f. wiss. Zool., Bd. xxv., p. 318. 



2 S. B. Akad. Wiss. Wien., Bd. 80, Abth. i., 1880, p. 238. 



