343 



the general accuracy of the description , it appears to me that he has 

 gone far towards proving that Phoronis is related to Balanoglossus, 

 using this name in its widest sense. The similarity is shown in the 

 existence, in Actinotrocha^ of divisions of the coelom corresponding 

 with the first , second and third body-cavities of Balanoglossus , the 

 proboscis-cavity being connected with the exterior by paired proboscis- 

 pores, and in the fundamental identity of the nervous and vascular 

 systems of the two types. Mr. Masterman is greatly to be congratu- 

 lated on the fresh light which he has thus thrown on the systematic 

 position of Phoronis. 



Mr. Masterman states that in his opinion the organ which I 

 formerly described 2 as the notochord of Cephalodiscus is not homolo- 

 gous with the notochord [Spengel's »Eicheldarm«) oî Balanoglossus, 

 but he regards it as the representative of a structure which he describes 

 in Actinotrocha as the »sub-neural gland«. The latter is supposed to 

 correspond with the organ of the same name in Ascidians and probably 

 with the hypophysis of the Vertebrata, and to be represented in Ba- 

 lanoglossus by the proboscis-vesicle (Spengel's »Herzblase«). It is 

 further concluded that Cephalodiscus and Actinotrocha possess paired 

 notochords, which in the later phylogenetic stage represented by Ba- 

 lanoglossus have fused together to form a single median organ. 



1 find myself unable to agree with the above-stated conclusions 

 in several respects; and my views may be formulated as follows: 



1) The median notochord of Cephalodiscus is really the homo- 

 logue of the «Eicheldarm« oi Balanoglossus. 



2) The comparison of the median notochord of Cephalodiscus with 

 the proboscis-vesicle or heart-vesicle of Balanoglossus is untenable. 



3) The proof of the homology of the so-called paired notochords 

 of Cephalodiscus and Actinotrocha with the notochord of higher Chor- 

 data is not convincing. 



1. Mr. Masterman remarks (p. 351) that the median notochord 

 of Cephalodiscus »presents no histological features resembling those of 

 every other notochord yet described«. If allowance be made for the 

 small size of Cephalodiscus , it is hardly surprising that its notochord 

 exhibits a comparatively simple structure; but I think that there is no 

 essential histological difference between this organ and the slender 

 anterior portion of the notochord in Schizocardium and Glandiceps, as 

 described by Professor Sp eng el 3. This fact by itself might be a mere 

 coincidence, but taking into account the relations of the notochord to 



2 Challenger Reports Vol. XX. Part 62, 1887. p. 40. 



3 Fauna und Flora G. v. Neapel, 18. Monogr., 1893. See p. 195, 196. PI. XII. 

 fig. 2, PI. XX. fig. 1, and elsewhere. 



