182 THE VOYAGE OF H.M.S. CHALLENGER. 



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 Ophiurans), in 

 which the young are carried about by the parents till they are well advanced Star-fishes 

 (Sars, Mliller, Agassiz), or hatched from the main cavity as well-developed Ophiuridse 

 (Quatrefiiges, Schultze, Lyman, Agassiz), and where the plutean development is passed 

 through in a very imj^erfect manner, owing to the rudimentary development of the arms, 

 which take such an extreme degree of growth in the pelagic pluteus of Echiuids and 

 Ophiurans, traces only of these arms being found in the younger stages of growth of 

 these viviparous Echinoderms. 



" The specimens I have had the opportunity of examining were collected at Kerguelen 

 Island 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 Hemiaster cordatus; but I cannot distinguish it from 

 Hemiaster cavernosus and Hemiaster australis, which I was led to consider (from 

 analogy with Hemiaster phili2^pii) to be identical species. It is remarkable that, in the 

 young stages of both these species, all the ambulacra are but little sunken, and it is only 

 when they have attained a considerable size that the 23osterior ones begin to deepen. 

 Philippi considered that 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 females. (See pi. iv. figs. 4-8, 

 Echini of " Hassler " Expedition, lU. Cat. Mus. Comp. Zool., No. 8). I have examined 

 a large numlier of a common Spatangoid from our southern coasts {Moira atrojyos), with 

 ambulacra still more deeply sunken than in Hemiaster, in hopes of finding the young, 

 but thus far without success ; from the eggs of Schizaster canaliferus from the Mediter- 

 ranean, in which some of the ambulacra are also deeply sunken, a pelagic jjluteus is 

 known to be developed ; so that in many of the genera with sunken ambulacral petals 

 the sunken area does not shelter the young in their earliest stages of development." 



Among the large number of specimens of this species collected by the Challenger there 

 were a few small specimens intermediate between the younger stages which I described in 

 the Proceedings of the Am. Acad, from specimens collected by Dr J. H. Kidder, U.S.N., 

 and those which were figured on plate iv. of the " Hassler " Echini in Mem. of Museum 

 Comp. Zoology. These figures I have reproduced (PL XX.* figs. 13-17), although they do 

 not quite fill the gap existing between the stage of Plate XX." fig. 9 and PI. XX.* fig. 18, 

 which were known before, still they leave but little to trace in the history of the development 

 of the petals, and of the gradual passage of the anal system from the abactinal surface to 

 the posterior edge of the test, and they also show the passage of the peripetalous fosciole 

 from that figured in stage 1.3 until it has assumed approximately the shape of the adult 

 (PI. XX.* fig. 18). The development of the males and females is identical to that point, 



