14 ON THE ECHINODERMATA OF THE 



The retractor muscles are thick and powerful, and attached along their length by 

 a muscular membrane to their corresponding longitudinal band. The whole muscular 

 system is very strongly developed, the longitudinal bands being remarkably thick and 

 robust, whilst the transverse series are numerous and closely placed. 



The Polian vesicles are long and thin, 10-15 in number, and of unequal length, the 

 longer ones being twice (or even more) the length of the shorter. 



The alimentary canal is nearly three times the length of the body, and is bent twice 

 upon itself. Passing from the mouth it runs four fifths the length of the body ; its 

 course is then reversed, and the canal proceeds as far as the anterior third of the body, 

 when it is again sharply bent backwards and passes to the anal extremity the three 

 lengths formed by the convolutions being held in their places by mesenteries. 



The mesenteries attached to the two lower portions are accompanied along the line 

 of their attachment to the body-wall by a longitudinal series of small pyriform bodies 

 of peculiar shape, attached to a common cord which passes nearly up to the oral extre- 

 mity the " infundibular " organs or " Wimpertrichter." Their form is represented in 

 Fig. 17; and it will be noted that they accord very nearly with those given by Sars of 

 C. pellucida, and in like manner with those of a Greenland specimen of C. Icevis, which 

 are figured for comparison. 



The generative organs consist of two series of long and extensive dichotomosing 

 tubes connected together by a slender branch. 



Size. The largest example of this species has been recorded by Sars, and measured 

 100 millims. in length ; generally, however, they range from 20 to 40 millims. 



Premature Form. In young stages the spots or sacculi which occur in the interradial 

 areas are smaller in number and proportionally larger in size than in the adult animal. 

 The calcareous wheels contained in the sacculi have both the spokes and the rim con- 

 siderably broader in the old than in the young form. Young individuals have also 

 fewer " fingers " on the tentacles, those of a small specimen 5 millims. in length having 

 only six digitations to each (Sars). 



Variations. Chirodota Icevis may unquestionably be regarded as a circumpolar 

 species; and the modifications which it presents are comparatively slight. We are 

 unable to consider the forms from Finmark and Lofoten, so carefully described by Sars 

 under the name of C. pellucida (Vahl), as other than the representatives of C. Icevis, the 

 Greenland type of Fabricius and Lvitken, the modifications which led Sars to place 

 them as distinct species being frequently found much less pronounced, in both forms 

 mutually, than in the specimens he examined. Amongst the specimens of this species 

 procured by the ' Valorous ' dredgings there are examples in which the form of the 

 wheels and of the tubular infundibular organs accord perhaps more nearly with Sars's 

 figures of C. pellucida than with those which he gives for comparison of the same 

 structures from the specimen of C. Icevis which he had dissected. Upon both of these 

 points he placed great importance. 



C. discolor, of Grube, from Behring's Straits, although presenting greater divergence 

 than the above, seems indubitably to belong to the same type. The differences noted 

 in the form of the wheels and the structure of the infundibular organs, as well as the 



