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not of quite the same kind as in Auriculariae and Echinoplutei. In the 

 larva of Echinocyamus pusillus I have found a simicircular streak in the 

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

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

 Clypeastroid-larvse, and also in the larva of Echinometra lucunter I have 

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

 it does not appear as a rule to exist in all Echinoid-larvse, but rather as 

 an exception. On the other hand MacBride has shown an apical nervous 

 system of more ganglionic structure to exist in the larvse of Echinus escu- 

 lentus and Echinocardium cordatum (for references, see my paper quoted 

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

 between these two nervous systems in Echinoid-larvse, how far they are 

 distributed within 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-larvse 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-larvse). Only a sub-epidermal network of nerve fibres 

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

 of Asterias rubens and Porania pulvillus. This fact tends to indicate that 

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



The intestinal organs are of a very uniform structure throughout the 

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

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

 larva of Colobocentrotus atratus and of a kind of gizzard-like structure in 

 the larva of Arachnoides placenta and, less distinctly, in some other Cly- 

 peastroid-larvse. 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 to 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, not 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 typical larvse as possible, this being the only way to 

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

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

 with abbreviated development, Peronella Lesueuri, Heliocidaris erythro- 

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



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