220 



While it would thus appear to be a rule that the larvae of the Phanero- 

 zonia have no Brachiolaria-stage, the facts known of the development of 

 the Spinulosa and the Forcipulata (Cryptozonia) seem to indicate that their 

 larvK are characteristic through having a Brachiolaria-stagei). The dif- 

 ferences between the various types of Brachiolarias are very unessential, 

 consisting mainly in the median Brachiolarian process being now round, 

 with a crown of papillae, now flat with a series of papillae along the edges; 

 this need not be considered here. The point to be emphasized is that the 

 Brachiolaria-stage is known to occur only in the more spec- 

 ialized Starfishes, and the Brachiolaria-arms and the suck- 

 ing disk connected therewith are therefore later acquired, 

 specialized structures. Accordingly the homology generally 

 supposed to exist between the sucking disk of the Brachio- 

 laria and the Pelmatozoan stalk is only apparent, and the 

 great part it has played in phylogenetic speculations is un- 

 justified, not being supported by facts acquired from an extended study 

 of the development of Asteroids. Of course, I agree that very much more 

 knowledge is needed for finally estabUshing this statement as a fact beyond 

 dispute. The metamorphosis of the Astropecten- and Lu zdia-larvae need 

 being studied in a much more detailed way than has hitherto been done. 

 It would also be of the greatest interest to study the development of such 

 Astropectinids and other Phanerozonia as have large, yolky eggs and to 

 see whether the larvae of such forms possibly develop Brachiolarian pro- 

 cesses and a sucking disk, as do e. g. the SoZas/er-larvae. If my views on 

 the development of Asteroids are correct, they should not develop such 

 processes, or, at least, no sucking disk. (Processes might not necessarily 

 be homologous with the Brachiolarian arms). Anyhow, the facts hitherto 

 known of Asteroid development seem to me to enforce the above conclu- 

 sions. 



It is of importance to notice the fact that during the metamorphosis of 



1) If the larva figured on p. 149 of my paper "Notes on the development and the larval 

 forms of some Scandinavian Echinoderms" really belongs to Stichaster roseus as supposed 

 by me there, that will be an exception to the rule indicated by the direct observations on 

 the development of the said groups of starfishes. I would not be inclined to think this prob- 

 able and therefore now doubt the correctness of that suggestion. The larva figured would 

 then belong to Astropecten irregularis. 



Gemmill in his paper on "The larva of the Starfish of Porania pulvillus (O. F. M.) (Qu. J. 

 Micr. Sc. Vol. 61. 1915) concludes from the fact that he has found this larva to have a Brachio- 

 laria-stage that "it is evident that the division of Asterids into Phanerozonia and Cryptozonia 

 is not necessarily associated with fundamental differences of development.'' As, however, 

 the position of the family GymnasteridfE (or Asteropidse), to which Porania belongs, within 

 the Phanerozonia is doubtful, this conclusion may not be justified. The fact of the Porania- 

 larva being a Brachiolaria at most may serve to prove that this larval stage makes its appear- 

 ance in the most specialized group of the Phanerozonia. 



