'21'.) 



seems fairly evidently U> belong lo Ibis same larval group. As might be 

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

 very elaborate structure. 



While in .1. nudibnincliidln the Auricularian type lias reached ils highest 

 perfection ( it is very interesting that also in regard to si/e this larva 

 represents the climax ), tin- Dendrochirole 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 1 )) or merely a reduced form, it would be of importance lo 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 Ilolothurians, it would not seem 

 unreasonable lo expect that such an interesting case might ultimately 

 turn up. 



The Bipinnaria in ils simplest type differs so slightly from the simpler 

 forms of the Auricularia lhal il may sometimes be difficult enough lo 

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

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

 ously regarded as one of the more primitive of recenl Asteroids, vi/.. Aslro- 

 peclen. It is especially an important fact that no Brachiolaria-slage occurs 

 in Ihis type of Bipinuaria. The same fad applies lo lhal more speciali/.ed 

 type, the Luidia-\ar\i\, in which the anterior part of Hie body has under- 

 gone a development into an apparently active swimming organ. Also Un- 

 remarkable Bipinnaria anlaniica recently described by Mac Bride 2 ) 

 evidently agrees with the Aslropcclen- and Luidia-\i\v\'<v in having no 

 Brachiolaria-stage, as MacBride justly infers from the fad lhal even in 

 a fairly advanced stage of metamorphosis the ventral median process 

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

 appeared. If Ihe reference of this larva to Chcinisler t/crlachci is correct, 

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

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

 laria?. This said larva represents the most speciali/.ed form of all known 

 Asteroid-larva in regard to Ihe vibralile band, which forms dense folds 

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

 Auricularia nudibranchiata, 



') Caswell Grave. On the oiTiirmirr amon^ Kchinodernis of Larv;c with cilia arranged 

 in transverse rings, with a suggestion as to their significance. Hiol. Hull. V. l!Ki:i. p. 169. 



-) E. W. MacBride. Echinodenna il'art II) and Enteropncusta. British Antarctic 

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



28* 



