1871.] 353 [Morse. 



or less conspicuous while still enclosed in the egg. Kupffer repre- 

 sents the same condition of things in his figures. x 



In the many free larvae examined by me, the axial segments were 

 perfectly defined. Fig. 2, plate I, represents two as they rested on 

 the slide. In these, forty segments were counted, four of these seg- 

 ments extending into the body proper, the anterior segment sending 

 off three diverging processes toward the haemal, or ventral region. 

 Beside the persistence of these segments after the animal was freed 

 from the egg, a remarkable structure not hitherto figured, as far as I 

 am aware, was noticed in the caudal fin, which vividly recalled the 

 fine diverging rays as seen in the embryo fish. These rays were 

 extremely delicate though plainly marked. They ran off nearly 

 parallel to the longitudinal axis of the tail, and were confined 

 to the last five segments, reaching beyond the last caudal seg- 

 ment, to a distance equal to eight segments, as shown in figs. 3 

 and 4. Those who have seen the caudal fin of the embryo trout with 

 its closely crowded ray lines, will bear witness to the strong similar- 

 ity between the two. At the junction of the tail with the body, a 

 series of rays of various lengths converging in pairs at the outer 

 border of the membran$ and running off at right angles to the longi- 

 tudinal axis, were also marked, though of extreme tenuity. This 

 peculiar feature is represented in fig. 2. All of the segments were 

 nucleated, and the tail appeared of uniform length. They were 

 enclosed in a continuous investing sheath which disappeared at the 

 caudal tip. This latter region was granulated. The peculiar black 

 spots, the 'sinnesorganej of which nothing is known, save that they are 

 supposed to be sense organs of some sort, were seen, but nothing defi- 

 nite was made out in regard to them. In fact the structure of the 

 fin only was studied. 



Since the above lines were written, Mr. Gavit has placed in my 

 hands for examination a number of embryos, from the same lot 

 studied, which ,he preserved in a saturated solution of salt and water. 

 These he has since mounted in cells with the same preservative fluid, 

 and though a year and a half has elapsed since these specimens were 

 immersed in the fluid, they are remarkably preserved and reveal cer- 

 tain features not recognized in the living specimens. 



Fig. 6 represents one of these preserved specimens. All traces of 

 segments have disappeared, the segments being irregularly broken 



iIbid.,Taf. ix, fig. 16. 



?KOCEEDINGS B. B. N. H.— VOL. XIV. 28 JUNB, 1872. 



