48 NATURAL SCIENCE. July, 



" In no group, perhaps, was our knowledge more extended by 

 the explorations of the "Challenger" than in that of the Ophiuroidea. 

 The number of known living species was increased from 380 to 

 about 550, or nearly by one half, while the corresponding increase of 

 novel groups is indicated by the addition of twenty genera. By far 

 the greater number of new species are of the deep-sea fauna ; that is 

 to say, they occur below the 100 fathom line, so that this Expedition 

 has furnished the first opportunity of comparing the littoral and the 

 deep faunae over a wide extent of the oceans of the world. The 

 result is that these Echinoderms are found to be animals which live 

 very much in defiance of temperature, light, and water pressure. 

 Something other than environment has determined their growth ; or 

 rather, their growth is not affected by an important part of their 

 environment. To be sure there are some genera which are con- 

 fined to the profound region of cold, darkness, and crushing weight; 

 such are OphiotrocJms, Ophioplintlms, and Ophiernus ; but there are 

 others, for example Amphiura and Ophiacantha, which are found from 

 the littoral zone down to the lowest points reached by the dredge. 

 In the different zones these genera may present modifications ; for 

 instance, the Amphiura', below 1,000 fathoms, often have more 

 numerous mouth papillae, and the corresponding OphioglyphcF usually 

 have swollen arm-plates and a microscopically tuberculous surface. 

 Such structural features, however, plainly have no connection with 

 the conditions of life, nor have they any relation to the survival of 

 specially favoured forms. From a depth of over 1,500 fathoms are 

 found the strongly armoured Ophiomusmm pitlchellmn [Fl. xi.,fig, 2), the 

 delicate Amphilepis, and the Ophiomitra chelys (PI. xi., fig. i), with its 

 thorny spines and soft disk. At that great depth the peculiar 

 conditions, apparently so unfavourable to a rich and varied growth, 

 have not checked the development of widely differing forms. 



" While, however, the Ophiuroidea yield little to the dictation 

 of light, heat, or water pressure, they show well-marked laws of 

 growth. Certain genera take the lead, like the larger clans of a 

 barbarous nation. The collections of the 'Challenger,' when com- 

 bined with those of the 'Blake,' show that the four genera 

 Ophioglypha, Amphiura, Ophiacantha, and Ophiothrix contain more than 

 two-fifths of the known species. There is a tendency also to 

 elaboration and variety in structure. The naked and embryonic 

 genera, like Ophiomyxa and Ophiogeron, have few representatives ; 

 while the finely constructed Ophioglypha has many species, and even 

 the highest group, composed of the closely allied Ophiura, Pectinura, 

 and Ophiopeza, is pretty strong in numbers. 



" The dredgings of the ' Challenger ' have further taught us 

 that we must not look exclusively in the abysses for surprising 

 shapes, or for those that connect us closely with geological times. 

 If the singular Ophiotholia must be sought in 1,800 fathoms, its 

 relative Ophiohelus may be found in less than 100 fathoms ; and if 

 Ophiomastus from the deep sea brings to mind the extinct Aspidura, 

 Pectinura of the littoral zone recalls the so-called Ophiura of the 

 Oolite. Nor must we forget that the extraordinary Astrophinra, 

 apparently intermediate between the Brittlestars and Starfishes, lives 

 in shallow water." 



Before the " Challenger " Expedition our knowledge of the 

 Holothurians was limited almost exclusively to littoral forms. By 

 the Expedition our acquaintance with these was greatly increased, 

 and an entirely novel fauna of the abyss discovered. The deep-sea 



