PROPAGATIOTSr OF CERTAIN ECHINODEEMS. 73 



tween them. While it is extricating itself, the oral surface of the 

 young is always above ; and the centre of the star with the mouth 

 is usually the part which fii-st protrudes ; then the arms disengage 

 themselves one after another, many of the brood remaining 

 for a time with one or two arms free and the others still under 

 the paxilli. When the young have become disengaged, they re- 

 main for a considerable time attached to the parent by the centre 

 of the dorsal surface. I could never satisfy myself by what means 

 this is effected ; the attachment is very slight, and they are re- 

 moved by the least touch. In this attached stage, until they en- 

 tirely free themselves, which they do when the number of tenta- 

 cular feet on each arm has reached about twenty, they cluster in 

 the reentering angles between the arms of the mother, spreading 

 a little way along the arms and on the dorsal surface of the disk ] 

 the young escape from the marsupium chiefly in the neighbour- 

 hood of the angles between the rays. The madreporiform tubercle 

 is visible in the young near the margin of the disk between two 

 of the arms ; but in the mature Starfish it is completely hidden 

 by the paxilli, and no doubt it opens into the space beneath 

 them. 



We took Archaster excavatus only on that one occasion ; and 

 the weather was so boisterous at the time that it was impossible 

 to trace the early stages in the development of the embryo. It is 

 evident that the process generally resembles that described by 

 Professor Sars in Pteraster militaris ; and it is quite possible that, 

 while there is certainly not the least approach to the formation of 

 a locomotive bipinnaria, as in that species some provisional organs 

 may exist an early period. 



In 'The Depths of the Sea' (p. 120) I noticed and figured a 

 singular little Starfish from a depth of 500 fathoms off the north 

 of Scotland under the name of Hymenaster pellucidus. This form 

 was at that time the type of a new genus ; but the researches of 

 the last three years have shown that, with the exception perhaps 

 of Archaster, Hymenaster is the most widely distributed genus of 

 Asterids in deep water. It is met with (sparingly, it is true, only 

 one or two specimens being usually taken at once in the trawl) in 

 all parts of the great ocean ; and it ranges in depth from 400 to 

 about 2500 fathoms. 



On the 7th of March, 1874, we dredged an extremely handsome 

 new form, to which I shall give provisionally the name of H, nohilis, 



