Angular Sea-Cucumher. 155 



the ' Cuvierian organs/ has received the trivial name ' Cotton- 

 spinner/ 

 For figures of the Cuvierian Organs, see Hunterian Catalogue, 

 vol. i. pi. 3; J. Miiller, Abhandluugeu Konigl. Akad. Wiss., 

 Berlin, 1853, p. 208. 



resemblance to the relation subsisting between the compound eye of a Star-fish, 

 carried at the apex of one of its rays, and its centrally-placed mouth. A double 

 nerve-cord beset with pairs of ganglia has been figured by Schmarda, I. c, Taf. viii., 

 fig- 83, c, in a Turbellarian, Sphi/rocephalus dendrophilm, as extending from the 

 region of the eyes and frontlet backwards to that of the pharynx, and lends an 

 additional feature of resemblance to the two sets of structures just compared to each 

 other. On the other hand, the Turbellarians, with the exception of the Nemertines 

 (see Keferstein, Zeitschrift fiir Wiss. Zoologie, xii. p. 68), and all the other Platyel- 

 minthes are sterelminthous, and contrast herein very strongly with the Echino- 

 derraata. 



Several points of resemblance have been pointed out by Dr. Charlton Bastian, 

 as existing between the Nematoids and the Echinodermata (see Phil. Trans., 1866, 

 pp. 622-627), and amongst these, the arrangement of the nervous system and of tlie 

 various systems of vessels and integumental pores, deserve especial notice. The 

 Nematoids further resemble the Echinodermata in the large size of their perivisceral 

 cavity, and the absence from it of any of the transverse compartments which are 

 so common amongst Annelids, and which so plainly show that they are, in Mr. 

 Herbert Spencer's language, 'tertiary aggregates.' But they differ from them, as 

 indeed from the Vennes also, very markedly, in not going through any metamorphosis, 

 and in the aljsence of cilia from their entire organism at all times of their existence. 

 The Acanthocephali, which have been placed together with the Nematoids and 

 Chaetognatha as forming the class Nem.itelminthes, difi"er from both these orders, 

 and resemble the Echinodermata in having their adult forms originating with a 

 provisional larva or pseud-embryo. 



Perhaps more points of affinity exist between the Echinodermata and the highest 

 class of Vermes, the Annelids, than between them and the lower classes just com- 

 pared with them. The resemblance of the Gephyrean Vermes to the Holothurioidea 

 is so striking as to have caused certain members of the order (or class 1), the Sipun- 

 culidae, to be ranked in former times with the Echinodermata ; and this resemblance 

 relates to matters of greater moiphological importance than the resemblances of 

 external form and of habits wliich are so obvious as existing between the Synap- 

 tidae and the Sipunculidae. The absence or presence of cloacal respiratory trees 

 is similarly correlated in the Holothurioidea and the Gephyrean Vermes with the 

 presence or absence of certain ciliated infundibula opening into the perivisceral 

 cavity. The existence however in the Sipunculidae of a system of internally ciliated 

 vessels, which, from throwing a ring round the oesophagus, whence prolongations are 

 given off into the interior of their peculiar tentacles, and to the skin, and upon 

 which contractile Polian vesicle-like sacs are develojjed, musb be taken to be homo- 

 logous with as well as partly analogous to the peculiar ambulacral system of the 

 Echinodermata, is of the very greatest importance as showing the real affinity 

 in question. It must here be said that the Tubicolar AnneHds, which attain a 



