94 ALICE L. EMBLETON n\ THE STRUCTUEE AND 



its natiiro seems to be entirely different from tliat in other animals. In the adult it 

 functions less as a circulatory system than as a hydraulic apparatus for expanding;; the 

 proboscis in the Echiuroidea, and the tentacles in the Sipunculoidea, where it is entirely 

 absent from the following forms, which have no tentacles ; Fetalostoma, Onchnesomn, 

 and Tylosoma. Similarly liere, in Echiurus unicmcfus, tlie absence of the vascular system 

 may he in direct correlation with the extrenie reduction of tlie proboscis. This view 

 gains some support from the fact that in tlie Priapuloidea, an allied group, where there 

 are no head appendages (such as proboscis or tentacles), there is no vascular system. 



Mr. Sliipley * has called my attention to the fact that Thalassetna vegrande, Lampert, 

 has no proboscis, and but for the hooks there is no external indication as to which is 

 the anterior end. 



Distribution and Jffinities. — Up to the present this species has only been met with on 

 the Japanese coast ; this is evidently the worm Willemoes-Suhm found there in great 

 abundance, and Drasche's two examples were collected by Dr. A. von Roretz on the east 

 coast of S. Japan ; my specimens came from Tokyo. 



The affinities of tlie Echiuroidea, as a whole, are doubtful, and different zoologists classify 

 them very ditferently. Korschelt and TIeider, after studying the development of the 

 group, say that, "as regards the position of the Echiuridge, we agree with Hatschek's f 

 view ; he sees in them a division of the AnneUda, and In'ings them in relation with the 

 Ghsetopoda. The form and internal organization of the larva, as well as the mode of 

 origin of the setae, seem fully to substantiate this view. Even though the segmentation 

 (metamerism) no longer exists in the adult animal, it was nevertheless established iu the 

 larva, just as in the Chsetopoda and Archiannelida. The loss of the segmentation and 

 the reduction of the setae, as well as the enormous extension of the prostomium, or so- 

 called proboscis, make the Echiuridae appear as somewhat moditied forms." This is 

 confirmed by Conn |, who, with Hatscbek, inclines to separate the Echiuroidea from 

 the Sipuncixloidea. Shipley, however, is of opinion that the resemblances between these 

 tAvo great classes outweigh the differences, and that the Echiuroidea are derived from 

 the Chaetopoda, the nearest ally lieing iStern(is2:i/s ; that the Sipunculoidea are also allied, 

 but have departed much further from the Annelid stock. My observations on this 

 Japanese Echiurid lead me to believe that the connection with the Sipunculoidea is slight, 

 and that the features which separate the two classes are I'undamental. 



As regards tlie affinities of this species with the other members of the genus, there are 

 several very imjiortant points of dilTerence, w^hich may even justify its being placed in a 

 new genus by itself: — (1) Unlike all other known genera of the Echiuroidea — with the 

 exception of the aberrant Saccosoma — it has no extensible proboscis, that organ being 

 represented merely by a short blunt prostomial lobe (PI. 7. fig. 2) ; (2) according to Shipley, 

 a closed vascular system is characteristic of all Echiurids, yet it is totally absent here — 

 this may be indicative of a very primitive condition, but, apart from that, it is, I think, a 



* " Report on the Gepliyrean Worms collected by Mr. ,T. Stanley Gardiner at Rotnma and Funafuti," Proc. Zool. 

 Soc. 1898, p. -)72. 



t " Ueber Entwicklungsgeschichte von Kcldnnts, etc.," Arbeiten zool. Inst. Wien, lid. iii. 1881. 



t " Life-history of Thalassema," Stud. Biol. Lab., Johns Hopkins University, Baltimore, vol. iii. 1886. 



