§ 86. THE ECHINODERMATA. 8T 



spirally, consists of a spongy substance, from which projects a lamina like 

 the lamina spiralis of the conch of a snail shell/^' 



In Spatangus, the toothless mouth opens into a delicate oesophagus 

 which passes insensibly into a long tube of nearly the same size. This 

 last makes two convolutions in its course, and sends off at about its anterior 

 fourth a very long caecum. The digestive canal, situated between the origin 

 of this caecum and the oesophagus, is of a dark color and has transverse 

 plicae, while the remaining portion below is smooth and of an orange hue.*"^ 



In the Clypeastridae, the numerous spiral turns of this canal are sup- 

 ported by many calcareous laminge situated upon the interior of the shell. ^'* 



In many species of Clypeaster, this canal has at its commencement, 

 transverse folds, and further on numerous lateral caeca, which are sepa- 

 rated from each other by laminas like those just described.''*' 



In the Echinidae the pharyngs has very thick muscular walls, and is 

 surrounded by masticatory organs. Upon it succeeds a proper oesophagus, 

 which, after a few convolutions, passes to the anus situated in the centre of 

 the back. The digestive canal is a caecum given off by this last, and 

 has many spiral turns in the cavity of the body.'^' 



In the Holothurioi'dea, the very muscular pharynx is surrounded by 

 the osseous circle. In the Holothurinae, the intestinal canal, which is long 

 and equal throughout, has many turns from behind forwards, ending at 

 last in a large cloaca situated at the posterior part of the body. But in 

 the Synaptinae, it is short and nearly straight, and terminates in an anus 

 having no cloaca.*^"' 



In the Echiuridae ^^' this canal closely resembles that of the Synaptinae. 



In the Sipunculidae it is long, making its first turn about the middle of 

 the body, and its second near the posterior extremity. The ascending 

 and descending portions of this last pass spirally around each other ou 

 their way to the anus which is situated on the ventral surface of the 

 body.^^'> 



§ 86. 



As to the glandular appendages of the alimentary canal, the salivary 

 orga?is are perhaps entirely wanting in these animals. 



In the Holothurinae alone, are there particular appendages opening into 

 its anterior portion, which could be regarded as organs of this nature. In 

 the different genera, species, and even individuals of this family, these 

 appendages widely vary as to form and number. 



5 Müller, Abhandl. d. Berl. Akad. ISil, p. 230, loc. cit. ; afterwards by Quay and Gaimard (At- 

 Taf. V. las zool. du Voyage de 1' Astrolabe. Zoophytes, PI. 



6 See Merkel, Syst. d. vergleich, Anat. IV. p. VI. fig. 2, PI. VII. fig. 3). The cloaca is always 

 65, a.T.d Delle Chiaje, Mevaor. &c. Tav. XXV. wholly attached to the skin by numerous tendinous 

 fig. 12 ; also Carus and Otto, Erläuterungstafeln fibres. In Chirodota fusca the intestine is spiral 

 z. vergleich. Anat. Hft. IV. Tab. I. fig. 25, and (Atlas zool. &c. PI. VIII. fig. 3) ; but in Synapta 

 Wagner, Icon. zoot. Tab. XXXII. fig. 8. The Duvernaea it is nearly straight (^Quatre/aifes 

 natui'e of the canal figured by Delle Chiaje is yet Ann. d. Sc. Nat. loc. cit. PI. II.). 



unknown. Ic arises from the first portion of the U See the remarks of Forbes and Goodsir upon 



intestine, and returns to it at its middle portion, the Anatomy of Thalassema and Echiurux (Ji'ro- 



It has not been mentioned by Meckel. riep's neue Notizen, No. 392, p. 273, fig. 12). 



7 Agassiz, Monogr. des ScuteUes, p. 1-1, PI. IH 1- The alimentary canal of Sipunculus nudus, 

 fig. 19, a. and of Ecliinorhyncus, has been faithfully de- 



8 Ibid. p. 17, PI. XXII. fig. 28 (Laganum and scribed by Delle Chiaje (Memor. &c. I. p. 9, Tav. 

 Melitta). I. fig. 5, 6 ; p. 126, Tav. X. fig. 11) and Grube 



9 See Tiedemann and Valentin, loc. cit. {MiUler^s Arch. 1837, p. 245, Taf. XI.). I have 



10 The digestive canal of the Holothurinae was found a similar intestine in Phascolosoma granu- 

 first figured by Delle Chiaje and by Tiedemann, latum. 



