IX ENTER0PNEU8TA— LITERATURE 595 



the collar of the Enteropneusta, and the two posterior sacs of the foi-mer with the 

 two trunk ccelomio 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 hydrocosl 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 Echinoderms 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 larvie. 



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

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

 ccelomic 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 larvae, 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 "■ "pulsating vesicle" occurs, apparently 

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



The Kelationship of the Enteropneusta to Cephalodiscus and Ehabdopleura 

 will be considered in the Appendage to this chapter. 



Literature. 



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



of Arts and Sc. Vol. IX. 1873. 

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



Microsc. Sc. {N.S.). Vol. SXIV. 1884. 

 j'fie later stages in the development of Balanoglossus KowalevsMi, with a 



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



{JSr.S.). Vol. XXV., Suppl. 1885. 

 Continued account of the later stages in the development of Balanoglossus 



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



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

 The ancestry of the Ghordata. 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. 

 E. Kohler. Recherches anatomiques sur une nouvelle espice de Balanoglossus. 



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



Internat. Monatsschr. Anat. Hist. 3 Bd. 1886. 

 A. Kowalevsky. Anatomic des Balanoglossus delle Chiaje. Mem. Acad. Imp. 



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

 A. Krohn. Beoiachtungen iiber Echinodermenlarven. Arch. f. Anat., Physiol. 



u. vjissensch. Med. 1854. 



