ECHINODERMATA. 5 



upper or anal surface. In the centre is the membranous 

 stomach, which has been stained pink, as also have been the 

 five csecal tubes ' diverticula ' radiating from it. A portion 

 of the integument has been preserved round the anus, into 

 which a black bristle has been inserted. From the intes- 

 tiniform portion of the digestive tract arise some tufted caecal 

 appendages. The tubes which are given off from the stomach 

 in the direction of each of the rays very soon divide into two, 

 each of which gives off a number of arborescent caeca, filling 

 up the whole cavity of each ray. At the base of each ray is 

 placed a pair of generative glands. Each gland is made up of 

 numerous caeca, converging to a duct opening at the base of the 

 ray. The madreporic tubercle is between the first and second 

 rays on the right of the preparation, counting from the top. In 

 each ray, and on each side of the median longitudinal ossicles, 

 may be seen numerous ' ampullae.' 

 Kolleston, pp. 141145. 



7. A Common Cross-Fish (Asterias rubens}, dissected to 

 shew its generative system. 



The dorsal portion of the integument, with the whole of the 

 digestive apparatus, has been removed. The generative organs, 

 ovaries or testes (the Echinodermata being 'dioecious'), are seen 

 to consist of bundles of arborescent caeca, two to each ray, each 

 bundle being attached at the base of the cavity which contains 

 the digestive caeca, one on each side of the median longitudinal 

 ossicles. The attached extremity of each gland indicates the 

 position of its duct, which opens at the base of each ray in the 

 inter-radial space. 



8. A Common Cross-Fish (Asterias rubens}, dissected to 

 shew its nervous system. 



The tube-feet have been removed. The nervous system 

 lies on the ventral surface of the animal, and consists of a 

 pentagonal ganglionated ring surrounding the mouth, from 

 which a single cord passes down the centre of each ray. 



9. A crinoid Echinoderm (Pentacrinus caput-medusce), 

 dredged off Barbadoes, 1869. 



10. A Sea-Urchin (Echinus sphcera), divested of its spines, 

 and dried. 



The exo-skeleton is an immovably articulated, inflexible 



