196 DESCRIPTIONS OF PREPARATIONS. 



adambulacral moveable spines has closed completely over the groove, thus 

 protecting the soft parts which it lodges. 



The pedicellariae may be seen strewn among the spines of the perisoma, 

 and upon the moveable adambulacral spines. It is possible that some of the 

 minute elevations among the spines are the incompletely retracted tubular 

 respiratory processes of the integument. 



The oesophagus is short and longitudinally plicated : the cardiac and pyloric 

 divisions of the stomach are partially separated by a circular fold, and the intestine 

 has a narrow plicated aperture into the stomach. The epithelium of the stomach is 

 stated by Hoffmann to be ciliated. 



The arborescent caeca in the arms with their ducts are suspended to the dorsal 

 perisoma by a couple of mesenteric bands. The cells in the caeca form entero- 

 chlorophyll, and tryptic, peptic, and diastatic ferments. They pour their secretion 

 into the stomach. 



The development of the genital glands is periodical : when sexually mature 

 they reach far down into the arms. They are branched glands alike in both sexes, 

 and are surrounded by a blood sinus. Each gland has a single duct in A. rubens y 

 but this duct opens by a sieve plate, i. e. a plate pierced by many pores. There are 

 ten plates corresponding to the number of the glands. They are placed inter- 

 radially and dorsally close to the bases of the arms. In most instances the genital 

 plate has only one aperture. These calcareous genital plates have been supposed 

 to be the homologues of the genital, i.e. basal plates of the apical system in 

 Echinoidea. It is certain however that this is not the case : and in Starfish in 

 which the apical system is retained in its typical form, no relation is observable be- 

 tween the genital apertures and the basals. Moreover in certain Starfish there is a 

 more or less numerous series of genital glands, each with its own aperture, extending 

 up the sides of the arms to a greater or less degree. In Asterina gibbosa the genital 

 apertures are ventral. The duct in Asterina pentagona has unicellular glands by 

 which the coat of the ovum is formed. These are probably present in other Star- 

 fish as well. Impregnation is external. 



General Anatomy of soft parts. Ludwig, Z. W. Z. xxx. 1878; cf. Carpenter, 

 Q. J. M. xxi. 1 88 1. Add on generative organs. Ludwig, on Asterina gibbosa, 

 Z. W. Z. xxxi. 1878. 



General minute Anatomy. Beitrage zur Histologie der Echinodermen, Hamann, 

 pt. ii. Die Asteriden, Jena, 1885. 



Digestive ferments. Krukenberg, Vergleich. Physiol. Vortrage, ii. 1882, and lit. 

 cited, p. 78. On colouring matters. Id. op. cit. iii. 1884, and lit. cited, p. 179. 

 Enterochlorophyll. MacMunn, P. R. S. xxxv. 1883; Id. P. R. S. xxxviii. 1885. 



39. COMMON EARTHWORM (Lumbricus terrestris, s. Agricola), 



\ Suspended by the anterior extremity to show its external characters. 



THE anterior region of the body tapers to a conical point : the posterior 

 is flattened dorso-ventrally and tapers abruptly. The first somite so- 



