266 



AMONG THE SEA URCHINS. 



We have recently taken several of them off St. Anne's pier, as 

 well as four different varieties of Echinoidea larvae {E. escidenius, 

 E. rniliaris^ E. cordatum^ and one species we were unable to 

 name). This latter had already begun to evolve the first part of 

 the future echinoid shell or test, the buccal plates of the future 

 mouth being just perceptible. It is only by taking a number of 

 these species in varying stages of their nomadic pluteus life, that 

 scientists have been able to follow their " strange, eventful his- 

 tory," which I shall now proceed to describe, for towards the end of 

 the larval condition only a few hours are required for the absorp- 

 tion of the flesh and entire calcareous scaffolding, and the pro- 

 duction of a young echinus differing greatly from the complicated 

 larva, and yet still unlike the mature animal, for the round shell is 

 gradually built up, plate after plate and spine after spine, from a 

 minute buccal membrane, Fig. 5, Plate XVIII. 



If the accompanying woodcut of 

 the '^Pluteus'' larva of the Purple 

 Sea Urchin, from the west coast of 

 Ireland, is turned upside down, the 

 likeness to a fireman's helmet will 

 be noticed, as it is drawn in profile ; 

 but if you will now turn to our 

 January illustration, Plate I., Fig. 5, 

 and turn it also upside down, for 

 our artists seem to have a difficulty 

 in sketching these forms the right 

 side up, you will perceive the simi- 

 larity, which the late P. H. Gosse 

 was the first to notice, to a painter's 

 easel, when looked at full in the 

 face ; for, he says,* " it consists of 

 four long legs or rods, arranged two 

 in front and two behind, with con- 

 necting pieces going across in a 

 peculiar manner, and meeting at 

 the top in a slender, pointed head." 

 "The whole calcareous framework 

 is invested with a clear gelatinous 



'^Gosse's Tenby, page 282. 



Fig. 5. — Pluteus Larva of Purple 



Sea Urchin [Str ongylocentrotus 



lividus). 



