434 MORGAN: [Vol. V. 



Spengel published a short paper on Tornaria in 1877, but I 

 have not been able to see this. Reference is made to it below 

 by Metschnikoff. 



The substance of it was, I believe, incorporated in Spengel's 

 latter paper in 1884. Alexander Goette published a brief notice 

 of a young stage of Tornaria in his paper on Comatula in 1876. 

 The figure is of a very young stage of Tornaria, and has been 

 copied into the text-books. The important structure that it 

 shows is the origin of the anterior enteroccel as an evagination 

 of the digestive tract. Without questioning that this may be 

 the real origin of the enteroccel, I do not believe, however, that 

 the figure shows this as pretended, but that the so-called evagi- 

 nation is only an artefact, and that the true enterocoel is shown 

 just above this already formed, and in close connection with the 

 muscle band from the apical plate. Balfour, in 1879, expressed 

 the opinion in his text-book that Tornaria is intermediate in 

 structure between the larva of the Echinoderm and the Trocho- 

 sphere type common in the Mollusca and Chaetopoda. The eye 

 spots, the muscle bands from the apical plate, and the circular 

 band of cilia, and the terminal anus are Trochosphere charac- 

 ters. Metschnikoff published in 1881 another paper on the 

 systematic position of Balanoglossus, which is one of the most 

 suggestive speculations about the group. Assuming the rela- 

 tionship of Tornaria to the Echinoderm larva, this necessitates 

 that Balanoglossus shall be referred to the Echinoderm type ; 

 and inasmuch as the fundamental form of the Echinoderm is 

 bilateral, this is not difficult. The water pore is the madre- 

 poric pore ; the proboscis corresponds to a single ambulacral 

 tentacle, and the blood-vessels find their homologues in the 

 Holothurian, as do also the peritoneal body cavities. The gills 

 of Balanoglossus are probably not new structures, but represent 

 the retarded and rudimentary portions of the water system, and 

 " it is interesting that according to the observations of Spengel, 

 the most anterior gill pouches communicate with the peritoneal 

 cavity of the collar, so that the gill openings function as the out- 

 let of the water vascular system." Also according to Spengel's 

 observations, the nervous system presents great similarities to 

 the same organ in Echinoderms. Balfour's comparison between 

 Tornaria and the Trochosphere will not hold, because the con- 

 tractile muscle band to the apical plate is not double, as in the 



