204 DEVELOPMENT OF AN AUSTRALIAN SEA-URCHIN, 



with quite ripe eggs. It was thus alone Toxocidaris eryihro- 

 graramus^ the development of which could be studied. But this 

 proved, in return, to be quite unusually interesting, so that it 

 was thought advisable to publish this short preliminary account 

 of it. 



The eggs of T. erythrogrammus* are large, ca. 0-5 mm. in diame- 

 ter, red-yellowish, and quite intransparent, evidently full of a 

 yolky substance; they are Jioating at the surface of the water, a 

 case not hitherto observed in Echinoderms. The cleavage is 

 total, and, in the first stages in any case, quite regular. The 

 gastrulse are not bound to the surface, but swim free in the 

 water, with the usual rotating movement. The aboral end, 

 which evidently contains the main part of the yolk, and thus is 

 the lighter end, is always turned upwards and remains so during 

 the whole of the development. 



Just above the oral end, a slight widening of the body of the 

 body of the embryo occurs, though not quite constantly, it seems. 

 This may perhaps represent a rudiment of the postoral larval 

 processes; but they do not dev^elop further, and there is no in- 

 dication of the typical Pluteus-shape at all; and, moreover, so 



*In Th. Whitelegge's " List of the marine and freshwater Invertebrate 

 Fauna of Port Jackson and neighbourhood" (1889), this species is men- 

 tioned under the name of Strongyloctntrotus erythroyrammus. As I have 

 shown in my work on the Echinoidea of the Danish Ingolf-Expedition 

 (Part i., 1903), the gewns, Strongylocentrotus must be restricted to a certain 

 group of northern species, the species drvehachiensis being the type of the 

 genus; the species erythrogrammus, together with several other species 

 from the Pacific, must be referred to the genus Toxocidaris. It is quite 

 probable that the name erythrogrammus will ultimately have to be changed. 

 The species figured under that name by Valenciennes (Voyage de la Fregate 

 Venus) is evidently the South American species Loxechinus alhus, and not 

 the common Australian species. Which name should then eventually be 

 substituted for erythrogrammus, I cannot say at present, having, of course, 

 no access to literature here. I may take the opportunity to point out here 

 that the other species of Strongylocentrotxts mentioned in Whitelegge's List, 

 Str. tubercidosus, is no true Strongyloctntrotus either; and, moreover, it is 

 by no means specifically identical with the conmion Japanese Toxocidaris 

 tuberculatus. What the correct name of this species will be, I am not 

 prepared to say at present, having not had the necessary literature or 

 time for investigating this matter. 



