Spicules of Cucumaria hijndmanni, &c. By Prof. Bell. 483 



impossible to forbear from some attempt to find an answer to a ques- 

 tion -which arises out of this remark, and which, being put generally, 

 may be thus expressed. How is it that in two allied species a 

 characteristic exhibits in one case constancy, and in the other 

 variability? A closer examination of the one now in question 

 seems to me to show us {a) that there is more variation in C. hynd- 

 manni than we should have been led to expect, and (/3) that 

 G. calcigera {G. horeni) has greater opportunities for variation, 

 thanks to the greater elaborateness of the spicules now being dealt 

 with. 



So far, I have endeavoured to direct attention to the specific 

 diflFerences between, and to draw such inferences as are most obvious 

 from the plates of these two northern species. This is neither the 

 suitable time nor place for entering upon the detailed examination 

 or recapitulation of such other points in the external or internal 

 anatomy, or in the " synonymy," which are important to the 

 systematic zoologist, but have no bearing on any sort of problem 

 that is presented to the microscopist. 



Yet another form of defensive spicule is to be found in a 

 specimen in the British Museum, which is registered as having 

 come from the coast of Jutland; presenting several points of 

 resemblance to the Cucumaria tergestina of Sars,* it is, strange 

 as it may seem, distinguished from it by the smaller size of the 

 plates in the integument ;t while I cannot feel that we should be 

 at present justified in uniting it with G. elongata ; at least if it 

 belong to that species the spicules of that " type " must vary con- 

 siderably in different individuals. 



The last set of spicules which I shall have to mention are those 

 here grouped as parts of fig. 4 a-^ ; they are taken, as are the two 

 which are marked 4a, from one of the specimens collected by 

 Colonel Montagu, which was in Leach's collection, and was 

 mentioned by Dr. Gray in the catalogue of British Eadiata, under 

 the title of Holothuria decollata. 1 had hoped by an examina- 

 tion of the spicules of this example to be able to set at rest the 

 very difficult questions that surround the determination of the 

 name of this form, which may conveniently be still called G. 

 montagui ; it will be seen, however, by the series of figures given, 

 that during the seventy years or more that this specimen has been 

 preserved it has been undergoing- some slow kind of maceration, in 

 consequence of which its spicules have become gradually broken 

 down, and a curious "dumb-bell" shaped form becomes the most 

 prominent, and apparently the most characteristic ; a similar kind 

 of change seems to have affected the rod-shaped spicules in the 

 suckers (fig. 4a). It is difficult to understand how this very gradual 



* Middelh. Fauna, p. 127. 



t The largest of those here figured is nearly a quarter of a millimetre long. 



2 I 2 



