219 



seems fairly evidently to belong to this same larval group. As might be 

 expected in such a specialized type, the calcareous bodies are wheels of a 

 very elaborate structure. 



While in A. nudibranchiata the Auricularian type has reached its highest 

 perfection ( — it is very interesting that also in regard to size this larva 

 represents the climax — ), the Dendrochirote larva represents the opposite 

 extreme, being simply worm-shaped, with none of the characters of the 

 Auricularia, its vibratile rings recalling those of the Auricularian pupa, 

 not the band of the Auricularia itself. For deciding the question, whether 

 this simple larva is a true primitive form (as maintained by Caswell 

 Grave^)) or merely a reduced form, it would be of importance to know 

 whether transitional forms exist, as is the case in the Ophiurans. Of this, 

 however, we are ignorant as yet; but considering the very imperfect stage 

 of our knowledge of the development of Holothurians, it would not seem 

 unreasonable to expect that such an interesting case might ultimately 

 turn up. 



TheBipinnaria in its simplest type differs so slightly from the simpler 

 forms of the Auricularia that it may sometimes be difficult enough to 

 decide to which of them such a form belongs. This primitive type is, as 

 far as hitherto known, peculiar to a genus of starfishes which is unanim- 

 ously regarded as one of the more primitive of recent Asteroids, viz. Astro- 

 peden. It is especially an important fact that no Brachiolaria-stage occurs 

 in this type of Bipinnaria. The same fact applies to that more specialized 

 type, the Luirfia-larva, in which the anterior part of the body has under- 

 gone a development into an apparently active swimming organ. Also the 

 remarkable Bipinnaria antardica recently described by MacBride^) 

 evidently agrees with the Astropeden- and Luidia-larvae in having no 

 Brachiolaria-stage, asMacBride justly infers from the fact that even in 

 a fairly advanced stage of metamorphosis the ventral median process 

 retains its typical shape, no trace of Brachiolarian arms having yet 

 appeared. If the reference of this larva to Cheiraster gedachei is correct, 

 we have here another case in support of the assumption that in the more 

 primitive Asterids upon the whole the larvae do not develop into Brachio- 

 larise. This said larva represents the most speciahzed form of all known 

 Asteroid-larva in regard to the vibratile band, which forms dense folds 

 or crenulations along the strongly developed arms, a case analogous to 

 Auricularia nudibranchiata. 



1) Caswell Grave. On the occurrence among Echinoderms of Larvae with ciUa arranged 

 in transverse rings, with a suggestion as to their significance. Biol. Bull. V. 1903. p. 169. 



2) E. W. MacBride. Echinoderma (Part 11) and Enteropneusta. British Antarctic 

 ("Terra Nova") Expedition, 1910. Zoology. IV. 1920. p. 90. 



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