DE\TELOPMENT OF .VISTEDOX (COMATXJLA, LAMK.) EOSACETS. 685 



ratus which are now generally admitted to entitle the CrinoI'dka to rank as a group of 

 ordinal value. 



The first approach to a knowledge of these peculiarities was made by Meckel', who 

 pointed out that the alimentary canal is provided with two orifices : the mouth, which 

 is nearly central, but inconspicuons ; and the anus, which is prominent but eccentric. 

 In ignorance, apparently, of what had been previously advanced by Meckel, Dr. J. E. 

 Gray^ in 1826 drew attention to the existence of a double orifice to the alimentary 

 canal, and to the importance of this character in classification. And in the same year 

 a more complete elucidation of this part of the structure of Comatula was effected by 

 Heusinger*. 



In 1827 the remarkable discovery was announced by Mr. J. V. Thompson^ (by whom 

 it had been made four years previously) of a true pedunculate Crinoid, to which he 

 gave the name Pentacrinus Enrojjcens, living in the Cove of Cork. His examination of 

 its structure enabled him to affirm its intimate resemblance, on the one hand to Coma- 

 tula, and on the other to the ordinary Crinoids ; and it is interesting to observe that he 

 had been led, by noticing its possession of a double oi-ifice to its alimentary canal, to 

 the recognition of the like conformation in Comatula — a discovery which was thus made 

 independently and neai'ly contemporaneously by Professor Meckel, Dr. J. E. Gray, and 

 Mr. J. V. Thompson. He does not limit himself to the description of that which he 

 considers the perfect form of this organism ; but gives an account, which though slight 

 is very characteristic, of the principal phases of its development, commencing with that 

 in w^hich " the animal resembles a little club, fixed by an expanded basis, and giving 

 exit at its apex to a few pellucid tentacula, no other part of the solid fabric being 

 observable but an indistinct appearance of the perisome ; " and he sagaciously adds, 

 " From these observations connected with the growth of this animal, and by which it 

 appears to present itself at various stages of its progress under considerable diversity of 

 form, naturalists may learn to avoid the unnecessary multiplication of the genera and 

 species of the Crinoidea by giving undue weight and consideration to characters ori- 

 ginating in the progressive evolution of individual species, and which are consequently 

 of a transitory and delusive nature." 



One of the most important contributions hitherto made to om- knowledge of the ana- 

 tomical structure of Antedmi, was the memoir of Heusingeb, ' Anatomische Untersuchung 

 der Comatula mediterranean published in 1829=. This is, for the most part, extremely 

 exact in its details, so far as these extend ; being chiefly deficient in regard to points 



' " Ueber die Oeffiiungen des Spcisckanals bei den Comatiden," in Meckel's ' Archiv fiir Physiol.,' Bd. VIII. 

 (1823) p. 470. 



= " Notice on the digestive organs of the gcmis Comatula, and on the Crinoidea of Miller," in 'Annals of 

 Philosophy,' N. S., vol. xii. (1826) p, 392. 



' " Bemerkungen iibor den Verdauungskanal der ComatuJen," in Meckel's ' Archiv fiir Physiol.' (1826), p. 317. 



* Memoir on the Pentacrinus Eui-opcem : a recent species discovered in the Cove of Cork, July 1, 1823. 

 With two pktes. By John V. Thompson, F.L.S. Cork, 1827. 



» Heusikger's ' Zcitschrift fiir organ. Physiol.', Bd. III. p. 366. 



