106 BULLETIN OF THE 



These are the most important references whicli have been found to the 

 embryology of this, one of our most common Ophiurans. My observa- 

 tions differ radically from the statements quoted. 



The eggs of Ophiopholis are cast free in the water, and the young pass 

 through a metamorphosis, in which a larva commonly called the pluteus 

 is formed. The mode of development of this pluteus is different from 

 that of any Ophiuran which has yet been described. It is most closely 

 allied to that of Ophiothrix, but in the mode of formation of a gastrula 

 differs widely from the account of a species of Opbiothrix. " 0. versicolor" 

 traced by Apostolides.* 



The formation of the gastrula in Ophiurans has been very unsatisfac- 

 torily studied. An invaginated gastrula has never been figured in this 

 group. Balfour f in a short notice states that he has observed in Ophio- 

 thrix that the gastrula stomach is formed as in other Echinoderms by au 

 invagination (of the blastoderm). The same mode had previously been 

 suggested as probable by many embryologists, and had found its way 

 into all the more important text books. It is not accepted by Aposto- 

 lides, one of the latest students of the development of these animals. 



Apostolides \ strongly combats the explanation of the method of for- 

 mation of the gastrula by invagination, and brings forward new observa- 

 tions on Ophiothrix, the same genus studied by Balfour, to show that 

 no invagination of the blastoderm occurs, and that the hypoblast of the 

 stomach is formed from cells in the inside of the blastosphere. To these 

 observations he brings as aids his studies of Amphiura to prove that in 

 Ophiurans the normal method of invaginated gastrulae does not exist. 



The observations, therefore, which I have made, are thought to have a 

 morphological importance as supporting the a priori views of most em- 

 bryologists, and the direct observations of Balfour on another genus, of 

 the method of formation of the stomach of the pluteus of Ophiurans by a 

 primitive invagination of the blastoderm. I have never observed the gas- 

 trula of Ophiothrix, and can speak with confidence of Ophiopholis only, 

 as far as this point is concerned. The differences between Apostolides' 



* le Th^se. Anatomie et D^veioppement des Ophiures. Arch. d. Zool. Exp. rf 

 Geu. X. Apostolides does not seem to hare suflBciently studied the descriptions of 

 the various species of Ophiothrix in the writings of Ljungnrian (Oph. Of Kong. Akiid. 

 p. 625, 1871. Description of 0. Lusitanka), and Lyman {Bull. Mus. Comp. ZoSi, 

 Vol. III. Part 10, pp. 240-249). The " 0. versicolor," Apostolides, is probably, as 

 has been suggested to me by Mr. Lyman, the same as 0. Lusitanka, Ljn. 



t A Treatise on Comparative Zoology. 



X Op. cit., pp. 192 and 207. 



