224 ENTEROPNEUSTA FROM THE SOUTH PACIFIC, 



species from the Marshall Islands should prove to be distinct, then its name (i.e. that 

 given by Eschscholtz) would have to be changed. This, however, was a mistake on my 

 part, since such a procedure would be contrary to the rules of priority in nomen- 

 clature. The present position of affairs with regard to this species is therefore, so far 

 as I am concerned, the following. Until it is shown that the Northern and Southern 

 species are different, Eschscholtz's name will apply to both. If, on the contrary, they 

 should eventually prove to be distinct from one another, then the Southern species 

 will be Pt. caledonica Willey and the Northern species alone Pt. flava Eschscholtz. 



TERMINOLOGY. 



Before proceeding further, I think it will be well to explain certain technical 

 terms which it is necessary to introduce when treating of the Enteropneusta in one's 

 mother-tongue. The combinations of native words which yield such impressive results 

 in other languages are not possible in English ; and, in any case, it seems only 

 reasonable that technical words .should be of such a nature, in respect of their ety- 

 mology, as to be available for universal use. 



I have already (loc. cit. 1897) translated Spengel's " Genitalfliigel " into genital 

 pleurae. More important is the rendering of Spengel's " Eicheldarm," since this involves 

 matter of controversy. It was Bateson who first advocated the view that this structure 

 is related to the notochord of the Vertebrates, and he, very naturally, called it noto- 

 chord. The notochord of the Chordata is a structure with which we are all familiar 

 and it is capable of exact definition. What has been called notochord in the Entero- 

 pneusta does not correspond with this definition except in its capacity of skeletal 

 product of the gut-wall. A special designation is therefore necessary, and the name I 

 propose for it is stomochord, the first half of the word indicating its relation to the 

 buccal cavity, and the second half indicating its resistent, chord-like character (cf. PI. 

 XXVI. Fig. 4). This term involves no sacrifice of conviction whatever, since it leaves the 

 question of the morphological relationships of the structure to which it refers quite open. 



The stomochord is not the only skeletal product of the gut-wall in the Entero- 

 pneusta. Spengel described in Pt. minuta a " kielfbrmiger Fortsatz des Darmepithels " 

 on the ventral side of the caudal region. Hill has found the same structure in Pt. 

 hedleyi, describing it as a " long and high keel-like process." I have found it in Pt. 

 flava, Pt. carnosa n. sp., and in Pt. ruficollis n. sp. It is a very remarkable structure 

 indeed and deserves to be called a pygochord. 



Spengel's longitudinal "Grenzwiilste" which characterise the lines of demarcation 

 of the branchial portion of the gut from the oesophageal portion in Ptychoderidae 

 are likewise structures to which I shall attribute a peculiar significance. They are 

 the parabranchial ridges. 



TAXONOMY. 



Spengel indicated clearly in his Monograph that the Enteropneusta are divisible 

 into three families, but he did not carry the matter beyond the point of naming one 

 family, viz., the Ptychoderidae. The deficiency may be supplied by naming the three 

 families as follows : I. Ptychoderidae, II. Spengelidae, and III. Balanoglossidae. 



