122 



A considerable number of Spatangoid larvae has been found in plankton 

 samples from various parts of the world. The study of these discloses 

 a remarkable uniformity in shape and skeletal structure. The presence 

 or absence of posterolateral arms appears to be an essential character, 

 distinguishing two main groups. Among those with posterolateral arms 

 the structure of the posterolateral rod may afford an important feature. 

 In some of them this rod is widened, tri-carinate at the base (Echinopluteus 

 fusus Mrtsn.), in others it is simple as in the larva of Echinocardium cor- 

 datum. The extent of fenestration of the postoral, posterodorsal and 

 posterior rods also affords specific characters, and Hkewise the shape of 

 the ventral transverse rods may be of importance. But, upon the whole, 

 these differences are so small and so unimportant from a morphological 

 point of view that I do not se any reason for describing the various 

 species found in my material. I would only point out that I have specimens 

 of the three said main groups both from the Atlantic, the Indo-Pacific 

 and from the Gulf of Panama. 



II. Ophiuroidea. 



While it is, with some very rare exceptions, a very easy thing to under- 

 take artificial fertilization of the Echinoids and to rear the larvae even 

 through metamorphosis, the Ophiuroidea in general resist artificial fertiliza- 

 tion. It appears next to impossible to find the eggs fully ripe and ready 

 for fertilization on opening the female specimens and taking the eggs 

 directly from the ovaries. Mostly they are found connected into clusters; 

 those few eggs which may be found lying isolated on the bottom of the 

 dish are not ready to accept the spermatozoa, and even being left some 

 time free in the water will not induce them to ripen, as is often the case 

 especially in Asteroids. Over and over again I have tried artificial fertiliza- 

 tion of Ophiuroids in this usual way, but always in vain, and it appears 

 that other investigators have had the same experience. Only with Ophio- 

 thrix fragilis (which I have not tried) it seems to be easier to obtain true 

 artificial fertihzation ; at least some authors (Selenka, MacBride, Carl- 

 gren) state to have succeeded in fertilizing the eggs of this species; Se- 

 lenka and Graeffe also have succeeded in doing it with Ophiura tex- 

 turata. 



By far the easiest way to obtain fertilization of the Ophiurids is this 

 to put a number of ripe specimens, males and females, together in a dish. 

 It may then happen that some of them will cast their sexual products; 

 probably it will generally be some male which starts to emit its sperm, 

 and then the sperm in the water acts as a stimulus inducing the female 



