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nol of ([iiik' the same kind as in Auriciilaric'C and lu'hinoplutci. In the 

 larva of luhinnci/dmus piisilliis I have found a siniicircuhir slieak in the 

 epidermis of the oral region, whieh is evidently a nervous structure (Op. 

 cit. p. 157, fig. 5); the same structure appears to exist also in some other 

 Clypeastroid-larvae, and also in the larva of Echinomelra lucunler I have 

 observed something evidently corresponding to it (PI. XII, Fig. 1). But 

 it does not ai)pear as a rule lo exist in all Echin()id-larva\ hut rather as 

 an exception. On the olher hand MacBride has shown an a[)ical nervous 

 system of more ganglionic structure lo exist in the larva; of Erlumis escu- 

 lenius and Echinocardium coidaUim (foi- references, see my paper quoted 

 above). It will he an object of considerable interest to study the relation 

 between these two nervous systems in Echinoid-larvtC, how lai- they are 

 distributed wiliiin this larval type and whether they may occur together 

 in one and the same larva or exclude one another. 



It is a very remarkable fact that the Asteroid-larva* do not appear to 

 possess anything corresponding to the nervous system of the three other 

 larval types. (Also the Crinoid-larvae have a fairly well developed nervous 

 system, but that is, of course, of quite another type than that of the 

 pelagic Echinoderm-larva). Only a sub-epidermal network of nerve fibres 

 and neuro-muscular cells have been observed by (iemmill in the larvae 

 of Asterias nibens and Porunia pulnillus. This fact tends lo indicate that 

 the Bipinnaria represents a more primitive type than the olher larvae. 



The intestinal organs are of a very uniform structure throughout the 

 whole of the Echinoderm-Iarvae; only a few rather unessential points may 

 be mentioned here, viz. the existence of a small distinct inlesline in the 

 larva of Coloboccnlrotus alralus and of a kind of gizzard-like structure in 

 the larva of Arachnoides placenta and, less distinctly, in some olher Ch'- 

 peastroid-larvae. The main interest as to the internal structures of Echi- 

 noderm-larvae is attached to the enterocoel and hydrocoel. and their 

 transformations during the growth and metamorphosis of the larva. Of 

 this, however, 1 have only made very few observations, it being out of the 

 plan of the present work to pay special attention lo these structures. That 

 would have meant such an increase in the extent of the work that it was 

 out of question merely for this reason, nol to mention the time that would 

 have been required for such a study. But, of course, it would be of the 

 greatest interest to study these developmental processes in so many dif- 

 ferent forms of the ly])ical larvae as possible, this being the only way to 

 ascertain which features are of general validity and which of only more 

 special value. — In the present work it is only the more exceptional forms, 

 with abbreviated development, Peronella Lesueuri, Heliocidaris crijlhro- 

 gramma and Ophionereis sqiiamulosa, which have been made the object of 



30* 



