106 Dr. W. C. M'Intosh on the Early Stages in 



the anterior end or snout (fig. 7), it is found to be surrounded 

 by a ring of cilia, and to have the digestive tract clearly de- 

 fined as a more opaque central mass, the eyes, in this position, 

 being placed outside the latter. Next day their powers of 

 progression have still further increased, and they course 

 throughout the vessel like a swarm of dancing particles. In- 

 stead of being nearly circular, the body is now more elongated 

 (fig. 8), the anterior end being blunter and rounder, the poste- 

 rior somewhat more tapered. A distinct constriction marks 

 the seat of the ciliated belt. When viewed from the front, the 

 rounded anterior end presents the appearance shown in fig. 9, 

 the very great length of the cilia being in sti'ong contrast Avith 

 the drawing of the same aspect at an earlier period. The body 

 is cellulo-granular, opaque in the centi-e, more translucent at 

 the edges, and, when crushed, resolves itself into nucleated 

 cells and granules (fig. 10). The anterior brush of cilia is 

 placed at some distance behind the anterior end, apparently 

 on the same surface as the large ciliated aperture, and hence 

 is not well seen unless the animal is tm'ued round on one side, 

 as in fig. 11. The anterior region of the digestive canal is 

 richly ciliated, and under favom-able pressure becomes everted 

 (fig. 12), but by what aperture (natural or artificial) I have 

 not yet been able to determine with precision. 



During the subsequent days, the body becomes more elon- 

 gated, the cutaneous tissues are differentiated, and the diges- 

 tive tract especially assumes a definite shape. Coarser granules 

 and granular cells mark the latter under pressure ; and it is 

 also distinguished from the paler body-wall by its deep-green 

 hue and the distinct contractions of its muscular investment. 

 The animal now feeds, and the intestinal canal holds numerous 

 granules and sand-particles. The large aperture towards the 

 posterior end is surrounded by a strong belt of circular 

 fibres. The anterior part of the body is still bluntly rounded ; 

 and the eyes are situated about midway between the tip and 

 the ciliated ring. The cilia of the latter have much increased 

 in length, so that under a powerful lens the animal somewhat 

 resembles a winged wedge. 



At the end of a fortnight they all showed a tendency to 

 perish without further differentiation of textm^es ; so that for 

 the present the inquiry had to be relinquished. 



Mr. Alex. Agassiz* makes a remark in regard to his form, 

 the youngest of which was much older than the most advanced 

 just described, which does not seem to coincide with my ob- 

 servations ; for, in describing its structure, he says, " There is 

 as yet no exterior communication from the digestive cavity, 



* Loc. cit. 



