219 



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

 expected in sueh a sjjecialized type, the calcareous bodies are wheels of a 

 very elaborate structure. 



While in .1. nmlibianchidUi the .\uricularian type has readied its hiitjiesl 

 perfection ( — it is very interesting that also in regard lo size this laiva 

 represents the climax - ). tlie Dendrochirote larva represents the opposite 

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

 Auricularia, its vibratile lings recalling those of the .Vuricularian |)upa, 

 not the band of the .\uricularia itself. P'or deciding the question, whether 

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

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

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

 however, we are ignorant as yet; but considering the very im])erfect stage 

 of our knowledge of the development of 1 iolothurians, it would not seem 

 unreasonable to expect that such an interesting case might ultimately 

 turn up. 



The Bipi n na ria in its sim|)lest type dilTers so slightly from the sim|)lei- 

 forms of the Auiicularia 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 nu)re primitive of recent Asteioids, viz. Aslro- 

 peclen. It is especially an important fact that no Hrachiolaria-stage occurs 

 in this type of Hipinnaria. Tlu' same fact applies to that nu)re s|)ecialized 

 type, the Liiidia-hiryA. in which the anterior part of the body has under- 

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

 remarkable Bipinndiin aidarclica recently described by MacBride^) 

 evidently agrees with the Aslropecten- and Luidia-larvx in having no 

 Hrachiolaria-stage, as MacBride 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 gerlachei is correct, 

 we ha\e here another case in support of the assumption thai iu Ihe nu)re 

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

 laria\ This said larva represents the most specialized form of all known 

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

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

 A uricularia niidihiunrhiata. 



') Oa.swcll (iiavc. On tlic ociniTriiic among Kfhinodernis ol Larva' with cilia arranged 

 in traiisviTsu rings, willi a suggi-slion as lo their signilicanei'. Hiol. Mull. \'. I'.MI.!. \t. 16it. 



-) E. \V. Mat-Bride. Echinoderma (Part II) and Enleropneusta. Hrilisli Antarctie 

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



28* 



