434 MEMOIRS OF THE AMERICAN ACADEMY. 



few convolutions. The anus terminates the short intestine as a broad opening ; the 

 edges of the walls are lined by powerful vibratile cilia. On the lower side we find 

 on each side of the median ventral vessel a series of small folds closely packed, 

 extending a short distance from the median line, forming a flat, corrugated band, 

 gradually becoming narrower towards the anal extremity, extending from the collar 

 to the posterior extremity ; this band is of a light dirty-pink color, and, flanked as it 

 is by the dark-green convolutions of the alimentary canal, is a prominent feature of 

 the ventral side. Balanoglossus can easily be kept alive ; I have kept them several 

 weeks in confinement in jars, of which the bottom was covered with sand. The pro- 

 boscis is kept continually expanding and contracting, and the sides of the body, 

 especially of the posterior extremity, are in incessant motion. 



Kowalevsky is inclined to associate Balanoglossus with the Annelids proper, and 

 not with the Nemertians, in spite of its proboscis and its want of bristles and other 

 appendages. This remarkable type recalls the Tunicates, from the nature of the 

 gills and their mode of formation. It has, like Echinoderms, a ring canal ; its larva is 

 eminently echinodermoid, allied to Star-fish larvae, which in their turn are more closely 

 allied to the larvae of Holothurians and Crinoids than to those of Echinoids and 



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Ophiurans. The larva is, however, most closely allied to genuine Annelid larvae, as 

 Loven's larva, though the close homology is not at first apparent, owing to the 

 disproportion in the development of the anterior and posterior extremities in these 

 two types. It has, like Loven's larva, the peculiar thickening of the outer wall 

 immediately below the two large eye-specks, as well as the muscular band leading 

 from them. Neither of the Annelids developing from these two larvae have any 

 bristles, and if Schneider is correct in assigning Polygordius as the adult of Loven's 

 larva, we find the explanation of the two cavities lined with cilia, which he figures on 

 each side of the anterior part of the body of Polygordius, as rudimentary gills still 

 in the condition in which they first appear in Balanoglossus in the Tornaria stage. 

 Both are distinctly articulated. The opening of the mouth and the structure of the 

 alimentary canal are strikingly similar. The collar, however, is a feature which we 

 find nowhere among Annelids except among the Sabellidae, Terebellidae, Serpulidae, 

 Maldaniae, and the like. The presence of gills as found in Balanoglossus is a feature 

 totally unlike that of any other group of Annelids, nor can we in any way homologize 

 the gills with the dorsal cirri found in any group of Dorsibranchiates, as in one case 

 they communicate directly with the oesophagus, in the other with the perivisceral 

 cavity. In a species of Tomopteris, which is quite common on our coast, I have 

 observed in the lateral appendages the openings first seen by Claparede, which might 



