114 Prof. W. Thomson on the Depths of the Sea. 



and arms are greatly reduced in size and development, the 

 stem is much branched, and its joints are indefinitely and 

 irregularly multiplied, which shows, in fact, all those pecu- 

 liarities which we are accustomed to associate with compara- 

 tive degradation in the animal scale. In the Tertiary forma- 

 tions there are only some obscure traces of one or two small 

 forms of the group. Rhizocrinus lofotensis of Sars stands 

 in nearly the same relation to the Bourgueticrinus of the 

 English Chalk as Bourgueticrinus to the Apiocrinites and 

 Millericrinites of the Oolite. It is much smaller ; the stem 

 is even larger in proportion to the cup and special organs 

 of nutrition ; and here alone among known Crinoids we meet 

 with a character which would indicate marked degradation — 

 an irregularity in the number of the arms, of which there are 

 sometimes four, sometimes five, and sometimes even six. It 

 looks like a Bourgueticrinus which had been going to the bad 

 for a million of ages, and was somehow getting worsted in the 

 " struggle for life." 



Rhizocrinus seems to be very generally distributed : Dr. 

 Carpenter and I dredged it last summer ofi' the north of Scot- 

 land; and about the same time Count Pourtales, who was 

 investigating the opposite border of the Gulf-stream in con- 

 nexion with the American Coast Survey, found it ofi" the reefs 

 of Florida. 



Two living stalked Crinoids are well known as Inhabiting 

 deep water in the sea of the Antilles, and apparently some 

 other localities in the Indian and Australian seas ; but they 

 belong to a parallel family, which has come down continuously, 

 usually represented by only a few species, from the period of 

 the deposition of the English Lias. The remarkable point is 

 the discovery of a representative, living at great depths in 

 modern seas, of a family which had dwindled away and appa- 

 rently become almost extinct before the formation of the older 

 Tertiaries. No discovery in natural science so suggestive as 

 that of the younger Sars had been made for many long years ; 

 it set many of us pondering on the distribution and conditions 

 of life in the depths of the sea. 



The questions involved are very complicated. The late 

 Prof. Edward Forbes was the great authority on the distribu- 

 tion of marine life ; he and his friend tlie late Dr. Robert Ball 

 initiated the use of the dredge ; and Forbes defined certain 

 zones of depth which he held to be inhabited by special and 

 characteristic groups of animals. The last of these was the 

 abyssal or deep-sea zone ; and he supposed that in this zone, 

 wliich extended downwards from the 100-fathom line, life 

 gradually became more and more scarce, till, at a depth of 



