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further the species with shortened development, Asterias Miilleri, groen- 

 landica, hexactis, through the fact that their rudimentary larvae have dist- 

 inct Brachiolarian processes, lend support to the suggestion that this larval 

 type is characteristic of the whole family Asteriidse. 



So little is known as yet of the development of Holothurians that 

 hardly anything can be concluded as to how far the larvae may be arranged 

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

 larva is all that is known of the Synaptids ; three larvae of the genus Holo- 

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

 whether they adopt a more complicate structure in their more advanced 

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

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

 but much stress cannot be laid on this fact. 



Of more weight is the fact that three different species are known of the 

 type Auricularia nudibranchiata, resembhng 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- 

 chiata 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 Auricularia antarciica, plicata and minor belong to the same group 

 as A. nudibranchiata, and then we would here really have a "family" of 

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

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

 band). But 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 the Dendrochirotes 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 Echinoderm-larvae, it is clear that it has no bearing on 

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



The Crinoids are the poorest of all Echinoderms in regard to the pre- 

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

 corresponding to the other four main types of Echinoderm larvae. 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 



