108 BULLETIN OF THE 



with the care and completeness I could have wished, I feel satisfied from 

 the examination of several of the young, at a very early period, that in 

 this case no provisional mouth, and no pseudembryonic appendages what- 

 ever are formed, and that the primary aperture of the gastrula remains as 

 the common mouth and excretory opening of the mature form." In a 

 larva of an unknown Ophiuran, Krohn * finds the first infolding, " Ver- 

 tiefung," in the position later occupied by the mouth of the adult. 



I am unable to quote any direct observations on the gastrula of Ophi- 

 urans to show that the primary opening or gastrula mouth becomes a 

 plutean anus. An anus is wanting in the adult Ophiuran. 



Although Apostolides criticises the explanation given by others of the 

 method of formation of the openings into the internal cavity (stomach) 

 of the gastrula by an invagination, he does not show how mouth or 

 anus is in reality formed. As he does not show the old view to be erro- 

 neous, and suggests nothing better, we must at present adhere to the 

 commonly accepted explanation. The interpretation of Metschnikoff, 

 who regards the first formed opening as a mouth, seems more reasonable 

 than to suppose with Apostolides that it is an anus. Whatever it may 

 eventually become, Metschnikoff 's suggestion, that it is formed by an 

 invagination, conforms with what I have observed in the gastrula of 

 Ophiopholis. 



In a short notice of the development of Ophiophragma, Professor 

 Kachtrieb t refers to a blastopore, and a stomach " enteron " iii its gas- 

 trula. No infolding of the blastoderm to form this enteron is recorded, 

 but the recognition of the primitive opening as a blastopore in another 

 Ophiuran genus is worthy of notice.^ I believe the gastrula stomach of 

 Ophiophragma will be found to be formed by invagination as in Ophio- 

 pholis. Professor Nachtrieb also studied the development of Ophiothrix, 

 but his mention is too short to give me any information as to how he 

 regards the gastrula stomach as formed. From what he does give it 

 is supposed that the stomach is developed in the same way as that of 

 Ophiopholis. 



Ophiocoma didelpht/s, Wyv. Th. See also general results of the voyage of the 

 " Challenger," by the same author, p. 241 et seq., Fig. 60. 



* Ueber einen neuen Entwickelungmodus der Ophiuren. Arch. f. Anat. Physiol. 

 «. Wiss. Med. 1857. 



t Johns Hopkins University Circular, March, 1885. 



J By a comparison of Apostolides' figures of Ophiothrix it will be seen that the 

 pluteus has pushed out the lateral arms to double the diameter of the body before 

 a mouth or any external opening into the cavity of the pluteus is formed. 



