37 



longer during the metamorphosis; in the oldest stage represented by 

 Tennenl (PI. 2. Fig. 20 of his "Kchinoderm Hybridization"), which is 

 somewhat more advanced in metamorphosis than the oldest larva figured 

 here, the primary lubefeel 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 posloral arms. The vibratile lobes are 

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

 in 7>//;/!cu,s/r.s. The dorsal lateral band is much folded and forms a pair 

 of lobes almost as prominent as in YY//j/;n/.s7r.s. Inside the preoral arms 

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

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

 cells is found below the band in the vibralile 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 Tennenl the vibralile lobes arc 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) Tennenl 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 larva? of this species is not in a suHicienlly good condition to allow 

 a renewed careful examination: on Ihe other hand my drawings from Un- 

 living specimens are so elaborate that it would seem excluded thai then' 

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

 may be separated of! from the vibralile band in a somewhat later stage, 

 as appears to be the case in Tennenl's figure 1 ), and in view of the fact 

 that epaulets are formed in the larva of Lylecli. anamesus (piclus) 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 Hybridi/alion" 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 fromoif Haiti (18 I.T N. 7.", :>3"\V.. 

 II. Blegvad, "Ingolf" ''"/, 1911) Ihe 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 Lytechinns Darii'i/iilns, that I cannot 



') This figure is somewhat diagrammatic and perhaps not quilt- convincing in regard to 

 this point. 



