EAKLY DEVELOPMENT OF CRIBRELLA OCULATA. 395 



is filled with hypenchyme of a very similar nature to that of the embryonic Cribrella. 

 Again, Appelloff, # in a recent work on development of certain Actinice, finds yolk 

 elements in the archenteric cavity, and there are numerous other instances of the 

 same kind. That the early development of Cribrella should approach that of 

 Alcyonaria and Zoantharia much more nearly than that of its echinoderm allies is 

 of itself sufficiently remarkable, but I think it quite probable that other echinoderms 

 will be found to have a development not unlike that described here. 



Comparison with other Asterids. 



Leaving out the earlier stages, we are in a position to compare this development, in its 

 larval stages, step by step with that described by other workers. It is equally undesirable 

 and impossible to pass in review the mass of embryological work in relation to the asterids. 

 Without underrating the value of the earlier workers, we may, without much error of 

 commission, take as our basis of comparison the work of Ludwig t on Asterina (which will 

 always remain the classic memoir upon asterid development), of MacBride J upon the 

 same species, of Goto § upon Asterias pallida and on Asterina,^ and of Bury II uponjBipm- 

 naria asterigera and other types. In the case of an asterid with a demersal larva like 

 Cribrella, namely, Asterina, we have the extremely accurate observations of Ludwig and 

 the exact application of the modern methods of differential staining and serial sections 

 by MacBride and Goto ; yet it cannot be said that the last word has been said, 

 especially with regard to the fate of the body-cavities. Hence the study of an allied 

 form like Cribrella should at least assist to make matters more definite. 



We may review the structure of the bilateral larva of Cribrella, after which it will 

 be possible to discuss how far its structure is of phyletic significance. If we glance 

 again at stage D we notice an organism slightly elongated antero-posteriorly and 

 slightly compressed bilaterally. At the anterior end the part which we can recognise 

 as the pre-oral lobe, by analogy with other forms having a mouth, is produced into a 

 dorsal and two central processes. Behind is a slight neck, followed by a disc-shaped 

 body. Externally the symmetry is perfectly bilateral. Coming to the interior, we find 

 a central mesenteron, around which are arranged certain ccelomic pouches, all of which 

 are destined later to separate completely from it. We recollect that one section of these 

 have all arisen from a large anterior coelom, and another section of them from a posterior 

 ccelom ; the former have never fused or joined up with the latter, and the two series 

 have remained perfectly distinct throughout the development. It is this feature, unique 

 amongst known asterids, which constitutes the main value of the Cribrella larva from 



* Appelloff, A., Bergen Museum, Aarbog, 1900. 



t Ludwig, H., "Entwicklungsgeschicte der Asterina gibbosa," Zeitsch.f. w. Zool., vol. xxxvii., 1882. 

 \ MacBride, E. W., " Variations in the Larva of Asterina gibbosa," Philos. Hoc. Camb., May 1894. 

 § Goto, S., Journal of the College of Science, Imp. Univ. Tokyo, Japan, vol. x. pt. iii., 1898. 

 || Goto, S., ibid., vol. xii. pt. iii., 1898 ; and Annotationes Zool. Japonenses, vol. ii. pars iii., 1898. 

 1" Bury, H., "Studies in the Embryology of Echinoderms," Quart. Journ. Micr. Sci,, April 1889. 

 ** Bury, H., "The Metamorphosis of Echinoderms," Quart. Journ. Micr. Sci., vol. xxxviii. 95-96. 



