HALF-HOURS AT THE MICROSCOPE. 377 



think, render it unnecessary to say much more about it in these 

 notes. 



There are few microscopic objects more instructive or beautiful 

 than these, especially when bleached. An amount of variety will 

 be found in the form, size, and direction of the spines on one of 

 these shells, which will afford much room for thoughtful reflection. 

 The function of those before us appears to be primarily that of 

 defence ; on either side of the median line, proceeding backwards 

 from the mouth, is a set, the components of which resemble tiny 

 ivory spoons. I expect these are to aid the creature in burrowing 

 into the sandy tracts in which it resides. Interspersed among the 

 latter are some straight and very slender ones, whose function I 

 take to be probably that of tactile organs, analogous to the 

 " Vibrissas " of higher animals. The spine-like scales of some 

 insects have a considerable general resemblance to the spines of 

 Spatangus ; this is well shown in the wing of the larger Midge, 



I do not know if there be sufficient difference in the spines of 

 Spatangi to enable us to discriminate species thereby. The one I 

 am most familiar with, and the commonest, is S. purpureus. 



Anguinaria dilatata (PI. XXII., Figs. 7, 8, 9). — There are two 

 well-marked species in this genus which are confounded together 

 by Dr. Johnston {Brit. Zooph., I., 290, and PI. L., Figs. 7 and 8). 

 These species are A. anguina., the common form, and the present 

 one, which is sometimes called A. spatulata. Prof. Busk has, with 

 his usual minute accuracy, described the anatomy of A. anguina 

 in an old volume of Trans, of the Microscopical Society of London. 

 The resemblance in this species to a snake is very striking ; the 

 tentacles, when partially protruded, simulating a many-forked 

 tongue. At the aperture of the mouth is a horny lower jaw, 

 horse-shoe shaped in its figure. Mr. Busk described and figured 

 the muscles which open and close this jaw ; they are attached to 

 its angle, and consist of a small abductor of two fibres, and a 

 larger adductor, fan-like in shape, on either side of the mouth. 

 The fibres composing these muscles are of the striped kind, indi- 

 cating the possession of will in the creature having them. The 

 long muscle, whereby the polype is withdrawn into its cell, is 

 peculiar, in that the fibres composing it are permanently separate ; 



International Journal of Microscopy and Natural Science. 

 Third Series. Vol. VI. z 



