156 Descriptions of Prepao^ations. 



For a discussion as to the nature of the functions of the Cuvierian 

 organs, whether they are to be considered as weapons of 

 defence, or as exciting organs in connection with reproduction, 

 or as dejiuratorj glands, see Semper, L c, pp. 136-142. 



considerable external resemblance to the lower Echinodermata, and especially to the 

 Crinoidea, by the peculiar (Capitibranchiate) arrangement of their respiratory organs, 

 possess structures which may with probability be considered to be rudimentary 

 representatives of the tentacular vascular system of the Gephyrei, and, by con- 

 sequence, of the ambulacral system of the Echinodermata. Professor Huxley, who 

 (Edinburgh New Philosophical Journal, Jan. 1855), has drawn attention to the resem- 

 blance of the branchial organs of a Tubicolar Annelid, described by him under the 

 name of Protula Dysteri, to the pinnate arms of the Crinoids, has figured from the 

 same animal, I. c, fig. 3 ?>, a structure exceedingly like a rudimentary circum-oral 

 water-vascular ring, with two stunted saccular appendages. This structure is de- 

 scribed by its discoverer in the following words : ' On the dorsal surface of the head, 

 a longitudinal canal, which sometimes appears to be ciliated, was visible at b, fig. 3 ; 

 posteriorly it divided into two branches, which dilated into granular coeca, nrranged 

 in a kind of festoon in the first segment of the thorax.' The presence of cilia is of 

 importance as differentiating this structure from the non-ciliated pseud-haemal vessels 

 both of Vermes and Echinodermata. It is possible that the somewhat similarly 

 situated and similarly obscure organ in Arenicola piscatorum (see Grube in V. Carua ' 

 Icones Zootomicae, Taf. ix., fig. i cc), may be, as has been suggested (Nat. Hist. 

 E.ev., Oct. 1861, p. 487), a rudimentary structure of the same import ; at any rate, 

 it is plain that the transition from the 'calcareous ring' with a Polian vesicle 

 appended to it, which has in the new Holothurian species, Rhahdomolgus ruber, 

 described by Keferstein (Zeitschrift fiir Wiss. Zoologie, xii., 1862, p. 34), taken the 

 place of the entire water-vascular system of other Echinodermata, to the glands 

 supposed to secrete the calcareous tubes of many Serpulaceae, and the homologous 

 excretions of certain Terebellaceae and their allies is but very slight. 



Grube has (Miiller's Archiv., 1853, Taf. ix. x., pp. 340-342), described in the 

 aberrant terrestrial Annelid, Peripatus Edwardii, a system of vessels, one of which 

 is dorsal, and two lateral, but none of which are branched or connected with each 

 other. The two lateral canals lie each on the outer side of the halves of the nerve 

 cord, which are in this Annelid, as in many Tubicolar species, widely divaricated ; 

 their calibre is considerably larger anteriorly than posteriorly ; the structure of 

 their walls is grumous or glandular, and no other contents than clear fluid could be 

 found in them. In relation with and probably in connection with these canals on 

 their under surfaces anteriorly, was a delicate looped tube ; and similarly constructed 

 tubes were to be seen also in the posterior part of the body in relation with the feet. 

 The lateral canals appear to be of different structure from the dorsal ; at any rate, 

 the absence of continuity between the two sets of vessels in a terrestrial Annelid 

 goes far towards doing away with the difficulty of homologizing the, probably, simi- 

 larly discontinuous pseud-haemal and ambulacral vessels of the Echinodermata with 

 the ordinarily continuous and closed system of pseud-haemal vessels in Annelids. 



The divarication of the nerve-cord into two halves observed in Peripatus Edwardii, 

 appears to correspond with the divarication from each other on the ventral surface 



