428 MORGAN. [Vol. V. 



teries, and is wide from side to side, but narrow from above 

 downwards. The body cavities form between them in the mid- 

 dorsal and mid-ventral line large blood-vessels. In the upper 

 part of the body cavities a few cells connect the somatic to the 

 splanchnic walls. The posterior body cavity, which is seen in 

 Figs. 63, 64, 65, is noticeably free at this stage from these 

 anastomosing cells, while the collar body cavities, as seen in 

 Figs. 58 and 59, contain a great number of branching cells. 



Sections between those of Figs. 64 and 65 show that in this 

 region the digestive tract has its walls folding in a very compli- 

 cated manner. The folding may be due, as Agassiz suggested, 

 to the pulling in of the anterior region of the digestive tract 

 during metamorphosis. The sections posterior to Fig. 65 are 

 much like this one, as the body cavities extend to the very end 

 of the embryo. The digestive tract opens at the posterior end 

 by a large anal opening. 



The Nassau Tornaria. 



A few specimens of a very large and interesting Tornaria, 

 caught in deep water (but at the surface) off Nassau, Bahamas, 

 have been given to me by Dr. H. V. Wilson. They were pro- 

 cured during May, I believe, and are approximately all in the same 

 stage of development. It is not my purpose to enter into a 

 minute description of this larva, but rather to call attention to 

 some of its more obvious peculiarities. These larvae measured 

 4 mm. in length. The external appearance seems very different 

 at first sight from the Tornaria previously described. This is 

 caused to a large extent by the peculiarities of the longitudinal 

 ciliated band. A careful study of the course of this ciliated 

 band shows, however, that in its essential features it reduces 

 back to the same plan, and the details in which it differs would 

 seem to have been acquired to fit it for a more perfect pelagic 

 life. Weldon found the same larva at Nassau in October, when 

 many were in process of transformation into Balanoglossus. 

 Those I have were caught, as I said, in May, and were all of the 

 same age and younger than those described by Weldon. Those 

 which were kept in the laboratory in dishes were, Professor 

 Brooks tells me, soon transformed into young Balanoglossus. 

 The arrangement of the longitudinal ciliated bands in this larva 



