SOME POINTS IN THE ANATOMY OP POLYCRffiTA. 267 



the heart in Balanoglossus, the structure which Bateson 

 believes to represent the vertebrate notochord. Professor T. 

 J. Parker 1 has already pointed out, in opposition to Bateson's 

 arguments, that the vessel which lies on the same side of the 

 intestine as the notochord in vertebrates conveys the blood 

 from before backwards, while the dorsal vessel in Balanoglossus 

 conveys the blood from behind forwards. In this respect the 

 dorsal vessel of Balanoglossus agrees with the dorsal vessel of 

 all other Invertebrata, and I am strongly of opinion that 

 Balanoglossus is constructed on the same plan as a Chsetopod. 

 I would consider the proboscis as the prseoral lobe ; the nerve- 

 cord in the collar and in the proboscis as the enlarged repre- 

 sentative of the supracesophageal ganglia. The circum- 

 cesophageal commissures are present at the posterior region of 

 the collar, and they unite into a well-developed ventral nerve- 

 cord. The great obstacle to this view is the presence of the 

 dorsal nerve-cord in Balanoglossus. But it may be pointed 

 out that this dorsal nerve-cord is much thinner and more 

 insignificant than the ventral, and that the ventral is in shape 

 and character the real continuation of the nerve- cord in the 

 collar. The absence of nephridia and the meaning of the 

 proboscis pore and proboscis gland are points which cannot at 

 present be explained on the view I have advocated. 



3. Neural Canals. 

 The texts for the few words I have to say on this subject 

 are two papers, one by Professor Mcintosh, 2 published in 1877, 

 the other by Dr. Emil Rohde, 3 published in 1886. The first 

 gives a brief account of the anatomical relations of the ventral 

 nerve-cords in the families of marine annelids, while the other 

 discusses the giant fibres of the nerve-cord in Aphroditidze. 

 These structures are asserted by Rohde to be nerve-fibres, 



1 "On the Blood-vessels of Mustelus antarcticus," 'Phil. Trans.,' 

 vol. clxxvii (Pt. II, 1886), p. 719. 



2 "Arrangement, &c., of Great Nerve-Cords in Marine Annelids," 'Proc. 

 Roy. Soc.,' Ed., 1877. 



3 ' S. B. d. Konigl. Preuss. Akad. d. Wiss.,' July 29th, 1886. 



