No. 3.] GROWTH AND METAMORPHOSIS OF TORNARIA. 433 



1863, but our present knowledge of the anatomy began with 

 Kowalevsky. 



Again, in 1869, Metschnikoff published a paper on Tornaria, 

 and here for the first time was the relationship between the 

 Tornaria of Muller and the Balanoglossus of Delle Chaije 

 pointed out. This paper is one of the most important con- 

 tributions to the subject. He confirms Midler's statement that 

 the longitudinal ciliated band develops before the circular band. 

 The paired gut pouches are more clearly recognized than by 

 Muller. The formation of the mesenteries and body mus- 

 culature is recognized ; also the formation of dorsal and ventral 

 longitudinal vessels. The pulsating heart is described as 

 having a sort of pericardium. The larva was kept for about a 

 month, and its transformation into the worm-like Balanoglossus 

 seen. A pair of gill pouches was described, and later the cili- 

 ated gill slits ; and their resemblance to the gill slits of Appen- 

 dicularia recognized. The resemblance of the Tornaria to the 

 Echinoderm larva is insisted upon, and therefore the relation- 

 ship of Balanoglossus to a Holothurian-like Echinoderm is 

 rendered very probable, and the author regards the muscular 

 proboscis as a large ambulacral foot. Metschnikoff traced the 

 formation of the musculature of the proboscis from the anterior 

 enteroccel, and points out that in the young Balanoglossus, at 

 least, it does not open in the anterior portion of the proboscis 

 as described by Keferstein, Kowalevski, and Agassiz. 



Alexander Agassiz published in 1873 a paper giving an excel- 

 lent account of the metamorphosis of the New England Tor- 

 naria. He recognized the relationship between Tornaria and 

 Balanoglossus that Metschnikoff had pointed out, and therefore 

 abandoned his former belief of the Echinoderm nature of the 

 adult of Tornaria. He verified many of Metschnikoff's and 

 Miiller's descriptions, and added that in the New England Tor- 

 naria four pairs of gill pouches arise almost simultaneously along 

 the oesophagus. He also saw the division of each gill slit into 

 two by the formation of the tongue bar, and described the 

 formation of the gill skeleton. Agassiz also saw the Tornaria 

 undergo its transformation into the small Balanoglossus-like 

 worm, and the change was described as taking place suddenly, 

 accompanied by an opaqueness of the body wall, and the pulling 

 in of the oesophageal part further into the body. 



