ix ENTEROPNEUSTA LITERATURE 595 



the collar of the Enteropneusta, and the two posterior sacs of the former with the 

 two trunk coelomic sacs of the latter. The two anterior sacs are in communication 

 with the exterior through the collar pores ; this communication (hydropore, water 

 pore) in the Echinodermata is usually limited to the left anterior sac, i.e. to the 

 left hydrocoel vesicle, but occasionally in Asteroids a matter of great importance 

 appears on the right side as well. 



From these considerations, it seems that the prospect of establishing a funda- 

 mental agreement in structure between the Enteropneustan larva and that of the 

 Echinodermata is very hopeful. This relationship between the Enteropneusta and 

 the Echinodermata seems to rest upon more solid ground than do any of the others 

 which have been attributed to either of these two groups. 



At the same time any attempt to compare adult Echinoderms with adult 

 Enteropneusta is at present completely futile. The Echiuoderms and Entero- 

 pneusta could, as far as we can see, only be genetically connected through some 

 common racial form far back in their phylogeny a form which corresponded with 

 the Tornarian and the Dipleurulan larva. 



Further, before we can feel any certainty on these questions of affinity, new and 

 more exact ontogenetic researches must be made. The origin of the proboscidal 

 coelomic vesicle of the Enteropneusta has to be established, as has also that of the 

 "heart or proboscis vesicle." Attention must be directed to the question as to 

 whether a preoral section of the body corresponding with the proboscis of the 

 Enteropneusta is present (if only as a rudiment) in the Echinoderm larva, as for 

 instance in the preoral section of the body in the Antedon larva (?), or in the larval 

 organs of Asterina and other Asteroids (?). With reference to the " heart vesicle " 

 we are reminded of the statement that a "pulsating vesicle" occurs, apparently 

 not of enterocoelomic origin, in Echinoderm larvse. This has to be confirmed. 



The Relationship of the Enteropneusta to Cephalodiscus and Rhabdopleura 

 will be considered in the Appendage to this chapter. 



Literature. 



Alex. Agassiz. The history of Balanoglossus and Tornaria. Mem. Amer. Acad. 



u f Arts and Sc. Vol. IX. 1873. 

 W. Bateson. The early stages in the development of Balanoglossus. Quart. Jonrn. 



Microsc. Se. (N.S.). Vol. XXIV. 1884. 

 The later stages in the development of Balanoglossus Kowalevskii, with, a 



suggestion on the affinities of the Enteropneusta. Quart. Journ. Microsc. Sc. 



(AT.S.). Vol. XXV., Suppl. 1885. 



- Continued account of the later stages in the development of Balanoglossus 

 Kincalcvskii and on the morphology of the Enteropneusta. Quart. Journ. 

 Microsc. Sc. (N.S.). Vol. XXVI. 1886. 



- The ancestry of the Chordata. Quart. Journ. Microsc. Sc. (N.S.). Vol. 

 XXVI. 1886. 



Gilbert C. Bourne. On a Tornaria found in British Seas. Journ. Mar. Biol. 



Assoc. (2). Vol. I. 1889. 

 R. Kohler. Rechcrches anatomiqucs sur une nouvelle espece de Balanoglossus. 



Bull. Soc. Sc. Nancy (2). Tome VIII. 1886. An almost identical work in 



Internal. Monatsschr. Anat. Hist. 3 Bd. 1886. 

 A. Kowalevsky. Anatomic dcs Balanoglossus dclle Chiajc. Mem. Acad. I/nji. 



Sc. St. Petersboury (7). Tome X. 1867. 

 A. Krohn. Beobachtungcn iiber Echinodcrmenlarven. Arch. f. Anat., Pliysiol. 



u. wisscnsch. Mai. 1854. 



