37 



longer during the metamorphosis; in the oldest stage represented by 

 Tennent (PI. 2. Fig. 20 of his "Echinoderm Hybridization"), which is 

 somewhat more advanced in metamorphosis than the oldest larva figured 

 here, the primary tubefeet or spines(?) of the young urchin having been 

 formed, the postero-dorsal arms are slightly longer, though still scarcely 

 more than half the length of the postoral arms. The vibratile lobes are 

 rather broad. The anal lobe has not its corners produced, as is the case 

 in Tripneustes. The dorsal lateral band is much folded and forms a pair 

 of lobes almost as prominent as in Tripneustes. Inside the preoral arms 

 there may be found a pair of small processes. There is a collection of red 

 pigment in the end of each arm and a conspicuous series of such pigment 

 cells is found below the band in the vibratile lobes and in the postero- 

 lateral lobes. Also in the frontal area a prominent cluster of pigment cells 

 is found in the midline, above the preoral band. 



In the figure quoted from Tennent the vibratile lobes are very insigni- 

 ficant, but instead there is a pair of epaulets so broad as almost to join 

 in the midline. Also in the text (p. 139) Tennent mentions the epaulets 

 as a normal feature in this larva. There is here a discrepancy between 

 our observations which I cannot quite explain; my preserved material 

 of the larvae of this species is not in a sufficiently good condition to allow 

 a renewed careful examination; on the other hand my drawings from the 

 living specimens are so elaborate that it would seem excluded that there 

 could be any misrepresentation here. It is possible that the large lobes 

 may be separated off from the vibratile band in a somewhat later stage, 

 as appears to be the case in Tennent's figure^), and in view of the fact 

 that epaulets are formed in the larva of Lytech. anamesus (pictus) it 

 is, indeed, very probable that they should also be found in this larva. 

 Further observations will be necessary for settling this point. 



In regard to the skeleton the presence of a posterior transverse rod is 

 of special importance. It ends in two simple, diverging branches, the 

 upper one of which is much the longer. In Fig. 5, p. 138 of Tennent's 

 "Echinoderm Hybridization" this transverse rod is represented as having 

 in the middle a process above and below. I have found it simple in the 

 specimens that I have reared. On the other hand I find in a specimen 

 of this larva found in a plankton sample from off Haiti (18° 43' N. 73°53"W., 

 IT. Blegvad, "Ingolf" ^7i. 1911) the posterior transverse rod to possess 

 a pair of similar processes, only much longer than shown in Tennent's 

 figure. This larva, which is in beginning metamorphosis, otherwise agrees 

 so well with the reared larvae of Lytechinus variegatus, that I cannot 



1) This figure is somewhat diagrammatic and perhaps not quite convincing in regard to 

 this point. 



