RECENT WORK ON THE PROTOCHORDA. 237 



Thus in Mastevinan's pleurochords we have, as I believe, the 

 representatives of the lateral pouches of the enteropneustic 

 stoiTJOchord ; while in Roule's ventral diverticulum we have 

 the representative of tlie ventral caecum of the stomochord.^ 



With regard to the structure in Actinotrocha which 

 Masteiman homologises with the so-called notochord described 

 by Harmer in Ceph alodiscus and by Fowler in Rhabdo- 

 pleura, but which he (Masterman) labels "subneural gland," 

 it is not easy to suggest a final explanation. Harmer^ has 

 pointed out its resemblance to the vermiform process of the 

 stomochord which occurs in the Spengelidse, and it may no 

 doubt be compared with this structure. 



What is doubtful is its primordial significance. As a first 

 step in the discussion, the name arbitrarily given to it by 

 Masterman should be dropped, because it involves a simple 

 begging of the question. 



The following proposition may therefore be stated cate- 

 gorically : — The "notochord" of the Pterobranchia represents 

 the vermiform process of the stomochord of the Enteropneusta 

 (S[)engeli(la3) ; but there is not sufficient evidence upon which 

 to found an opinion as to its antecedent history. 



In the ])rocess of regional differentiation of the entire body, 

 which is such a characteristic feature of tlie Enteropneusta, the 

 part of this influence devoted to cephalisation has, as has been 

 already mentioned, led to serious changes at the anterior end 



^ The above view gives an adequate explanation of Roule's ventral diverti- 

 culum sufficient at least to show that the extraordinary theoretical excursion 

 which this author makes is quite superfluous. Roule compares Actinotrocha 

 directly with the Vertebrates because the Enteropneusta are " quelque peu 

 aberrant." As a fact there is, in my opinion, reason to suppose that the 

 Enteropneusta are even nearer the direct line of Craniate descent than 

 Amphioxus. To set aside the Enteropneusta as aberrant forms argues 

 ignorance of the group. 



Reference. — Louis Eoule, " Sur la place des Phoronidiens dans la 

 classification des auimaux, et sur leurs relations avec les Vertebres," ' C. R.,' 

 t. cxxvii, 1898, p. 633. 



- S. F. Harmer, "On the Notochord of Cephalodiscus," 'Zool. Anz.,' 

 1897, p. 3i2. (Masterman's reply thereto, ibid., p. 443.) 



