OF ARTS AND SCIENCES. 235 



Ilemiaster connected, so to speak, with the abactinal system is a most 

 interesting feature, as well as the complete separation of the bivium 

 and trivium, the origin of which among Echini had not been under- 

 stood. The whole family of Collyritidae, in which this is the normal 

 state, appear in geological times as an abnormal group, disconnected 

 entirely, and isolated from all the other Spatangoids, which it precedes 

 in time, and seeming thus far to have no connection with the Spatan- 

 goids of later geological periods. Their connection as an embryonic 

 stage is now clearly shown by the young of Ilemiaster here figured, 

 as well as the close relationship existing between the regular Echini 

 and such Spatangoids as CoUyrites, appearing as the earliest geologi- 

 cal representatives of the Spatangoids. The Collyritidas are, there- 

 fore, not structurally so far removed as has been generally supjiosed 

 from the regular Echini. 



The earlier development, that preceding the stage when the em- 

 bryo esca^ies in to the ambulacral area, could of course not be traced 

 satisfactorily. But enough could be seen of the shape of the embryo 

 mass to render it highly probable that the development was very 

 similar to that of other viviparous Echinoderms (Star-fish and Ophiu- 

 rans), in which the young are carried about by the parents till they 

 are well advanced star-fishes (Sars, Miiller, Agassiz), or hatched 

 from the main cavity as well-developed Ophiuridae (Quatrefages, 

 Schultze, Lyman, Agassiz), and where the plutean development is 

 passed through in a very imperfect manner, owing to the rudimentary 

 devolopment of the arras, which take such an extreme degree of 

 growth in the pelasgic Pluteus of Echini and Ophiurans, traces only of 

 these arms being found in the younger stages of growth of these vivi- 

 parous Echinoderms. 



The specimens I have had the oi^portunity of examining were col- 

 lected at the Kerguelen Islands by Dr. J. H. Kidder, the Naturalist 

 attached to the Transit of Venus Expedition, and were sent to me 

 for examination by Professor Verrill. He has described the species as 

 new, under the name of H. cordatus ; but I cannot distinguish it from 

 Hemiaster cavernosus and H. Australis, which I was led to consider 

 (from analogy with H. Philippii) to be identical species. It is re- 

 markable that, in the young stages of both these species, all the ambu- 

 lacra are but little sunken, and it is only when they have attained a 

 considerable size that the posterior ones begin to deepen. Philippi con- 

 sidered this might be a sexual feature. We have not sufficient data to 

 decide the question, but can only say that up to a certain size, at any 

 rate, there is no difference in the depth of the ambulacra of males and 



