Common Crossfish. in 



44. Common Crossfish [Asterias Rubens), 

 Linn. (Dried.) 



The animal consists of a central disk which is prolonged into five 

 lobes^ the so-called ' arms' or ' rays/ One surface of the specimen 

 is hollowed out into a deep central cavity eorresj^onding' with the 

 mouth, and made pentagonal by the abutment upon its edge of 

 the rows of spines bounding the five ' avenues/ which radiate out 

 from it on the same surface, and, from lodging- the locomotor feet, 

 have given this aspect of the animal the name of ' ambulacral.' 

 The other surface is more or less convex, and beset with spines ; 

 and in one of its interradial spaces it carries the concentrically 

 striated disk known as the ^madreporic tubercle.' The two surfaces 

 are nearly equally developed in Asteriae and Ophiurae. Along the 

 middle line of each radial avenue there runs a central furrow, 

 formed by and at the junction of the Vertebral' ambulacral os- 

 sicles. In this central furrow were lodg-ed first and most superiorly 

 the water-vascular canal supplying the ambulacral sucker-feet; 

 then some transverse adductor muscles; and thirdly and most 

 superficially, the gangliated nerve cord, the ' Ambulacral-gehirn ' 

 of the German writers. Externally on either side to this central 

 furrow, the lateral processes of the ambulacral ossicles form, by the 

 apposition of their emarginated edges, two alternately placed series 

 of conjugate foramina, for the vessels bringing the sucker-like 

 exteriorly- placed portion of the feet into communication with in- 

 ternally placed ampullae as seen in Preparation 45. These am- 

 pullae are wanting in the Ophiui-ae, as also in the ambulacral 

 tentacles of certain Holothurioidea, for which see Preparation 47. 

 Each of tlie five radial avenues tapers up to its distal extremity 

 where the eye was lodged, and where in the fresh specimen the 

 suckers may be observed to attain a considei'able relative length. 

 On each side of each avenue we see two sets of spines, one of 

 which is placed internally, and consists of two rows of long and 

 slender spines ; whilst the more externally placed one is made up 

 of three rows of stouter, shorter, and blunter spines. Towards the 

 apex of each ray the external set of spines attains a greater de- 

 velopment relatively to the internal ; and out of it is there evolved 



