No. 3.] GROWTH AND METAMORPHOSIS OF TORNARIA. 4 19 



were united across the apical plate would then be spoken of as 

 postoral. 



Now if in the younger stages the bands actually crossed 

 from right to left, I think we would expect them to be actually 

 united in the older forms across the apical plate from right to 

 left ; but since each ends abruptly in these older stages, it seems 

 to me to indicate a secondary change. Consequently I think it 

 more probable that the longitudinal bands go through exactly 

 the same changes that we find in the typical Echinoderm larva ; 

 viz. at first a simple continuous band, and secondarily a fusion 

 of the two with the apical plate, resulting later in a new arrange- 

 ment of the bands. In the Tornaria, however, the fusion of the 

 bands must occur very early, or at the very beginning, for in the 

 youngest larva figured they are already found. Later there is 

 seen a tendency to unite from right to left in the Tornaria, and 

 this is actually accomplished in the Echinoderm larva. 



The two eyes are semi-circular bodies right and left of the 

 median plane, surrounded by a semi-circular zone of pigment, as 

 seen in Fig. 7, and on an enlarged scale in Fig. 43, PL XXVII. , 

 which is also a surface view. The details of the eye are best 

 seen in Fig. 44, which is from a section parallel to the upper 

 surface of the apical plate. The clear crescentic portion is seen 

 to be formed by a series of rod-like bodies, each being contin- 

 uous on its outer end with a pointed bristle-like portion. The 

 bristles seem to be cuticularized, and each ends in a sharp point, 

 the points being drawn together at a central point. The 

 clear rod-like portions of the cells cannot be traced after they 

 enter the pigment zone, but undoubtedly the nuclear ends of 

 the cells lie here. Fig. 44' is the next section beneath 44. In 

 this the clear inner portions of some of the cells are still seen, and 

 near them in the pigment zone a few large nuclei, which I am 

 inclined to believe belong to the inner ends of the eye elements. 

 Whether the pigment is in or between the retinal elements I 

 could not determine, but judging from the quantity, I think 

 much, if not all, belongs to the inner ends of the elements. There 

 is seen in Fig. 44', on the concave side of the eye, a collection 

 of small nuclei, but these do not seem to belong to the eye 

 itself. It seems probable, then, that each element of the eye 

 consists of a nucleated and pigmented inner end, followed by a 

 transparent rod-like portion, and ending in a bristle-like point. 



