127 



To this same larval type further belongs the larva of Ophiothrix angu- 

 lata Say (Var. poicila H. L. Clark), which I succeeded in rearing during 

 my stay at Tobago, B. W. I. in April 1916. Ripe specimens of this species 

 were secured on April 1 1th, which gave off sperm and eggs ; the eggs were 

 shed all at the same time, almost as by an explosion. The first development 

 processes pass very much in accordance with what is known from 0. fra- 

 gilis. At the age of 18 hours the embryos were found to be lenticular in 

 shape, but still without skeleton. At the age of 24 hours they were already 

 small plutei with fairly long posterolateral arms, the other arms not yet 

 having appeared (corresponding to the stage represented in PL 31. Fig. 6 



Fig. 53. Skeleton of Ophiopluteus of Ophiothrix, species a. ^'"/i- 



of MacBride's memoir on the development of Ophiothrix fragilis^), which 

 is, however, much older, 55 hours). At the age of 40 hours the postoral 

 and anterolateral rods had begun to form, the corresponding arms being 

 as yet merely indicated, while the posterolateral arms are already of con- 

 siderable length; their rods are still without thorns. The larva in this stage 

 is exceedingly characteristic, the preoral and postoral band continuing 

 almost straight across the anterior edge of the body (PI. XX, Fig. 1). At 

 the age of 4^/2 days the larvae had reached nearly their full shape, only the 

 inner arms not having attained their full length (PI. XX, Fig. 2). Thorns 

 had begun to appear on the posterolateral rods; the median process from 

 the transverse rods had not yet been formed. A small group of red pig- 

 ment grains is found near the base of the posterolateral arms, and there 



meaning was, of course, tiiat it is impossible to decide to which species it belongs, as it could 

 hardly be doubted that it must belong to some species of the genus Ophiothrix. 



In the "Echinodermenlarven d. deutschen Siidpolar-Exp edition" (1913 p. 98) this larva 

 was recorded from off Ascension. 



1) Quart. Journ. Micr. Science. Vol. 51. 1907. 



