21G 



further the species with shorteiuMl (livelopment, Asterias Mitllcri, groen- 

 landira, he.Ktclis, Ihroiij^h the fad that their riKhnu'iitary larva' have dist- 

 inct lirachioiariaii processes, lend support to the suj4i»eslioii Ihat this larval 

 type is characteristic of the whole family Asleriida'. 



So little is known as yet of tin' (levelo|)inenl of Holothurians that 

 hardly anything can he concluded as to how far the larva- may he arranged 

 in groups, corresponding to the orders or families of the adults. A single 

 larva is all that is known of the Synaptids: three larva* of the genus Ilolo- 

 Ihuria are known, but none of them in their full shape, and it is uncertain 

 whether they ado|)l a more complicate structure in their more advanced 

 stages. That they aie very much alike in the younger stages, all being of 

 a very simple shape, is in good accordance with wiial should be expected, 

 but much stress cannot be laid on this fact. 



Of more w\>ight is the fact that three different species are known of the 

 type Aniiculdiia midibiaijchiala, resend)ling one another so closely that 

 it is difficult enough to distinguish them. This proves that we have here 

 a case of the larvae of closely related species agreeing very closely in their 

 characters. (Although we do not know to which genus the A. nudibran- 

 chiala belongs, there can hardly be any doubt that all these larval species 

 belong within the same genus, or, at least, — in case MacBride's state- 

 ment that the intestinal pouch of species c is a paired organ be correct 

 — very closely related genera). It would not seem unreasonable to suggest 

 that Auricuhtrid (inldirlicd. plicula and minor belong to the same group 

 as .1. niidibianrliiaUi, and then we would here really have a 'family" of 

 Holothurian-larvcV, fairly well characterized through several features (e.g. 

 the peculiar shape of the oral region, the peculiar folding of the vibratile 

 t)and). Hut as long as we do not know anything with certainty about the 

 parentage of these larvae, we may only hint at this as a possibility. 



It appears to be a rule that llic Dendiochirotes have a shortened devel- 

 opment, without a typical pelagic larval stage. Without entering here on 

 a discussion of the question, whether the simple larva of the Dendrochi- 

 rotes is a secondary adaptation or whether it represents the most primi- 

 tive condition of Kchinoderm-larvse, it is clear that it has no bearing on 

 the problem of the classificatory value of the typical pelagic larvae. 



The Crinoids are the poorest of all Kchinoderms in regard to the ])re- 

 sent subject, as we do not know one single truly pelagical Crinoid-larva, 

 corresponding to the other four main types of h>hinoderm larva\ Till now 

 only Comatulids have been studied as regards their development, and it 

 seems very likely that within this whole group the development is of the 



