148 s. GOTO. 



means of which the worm can attach itself to foreign bodies sufficiently 

 firmly as to drag its body after it. AVe are therefore compelled to 

 admit the suctorial action of l^oth the anterior and the posterior suckers. 

 This action I shall n(3W proceed to explain. 



The so-called chitinous rods and pieces that compose the sup- 

 porting frame- work of the suckers are, as I have already stated, not 

 formed by true cliitin, but are soluble in caustic potash, and in some 

 species stain more or less, and do not ^ieem to be rigid. On the contrary, 

 I believe they are easily flexible but elastic, so that when distorted 

 by external fjrce they constantly tend to resume their original form. 

 In fact, if a living worm be observed under the microscope the suckers 

 are seen to constantly change their form; and this seems to be im- 

 possible if the so-called chitinous frame-work be perfectly rigid. I also 

 believe that the prismatic fibres which compose the wall of the suckers 

 are likewise elastic; this seems to be very probable from their great 

 (douljly?) refractive power and from their other optical characters. 

 Tlie image, then, I form of the suckers from the physic^logical 

 point of view is that of a bag (hemispherical or rectangular) with 

 a thick, elastic wall which constantly tends to be flattend out, but 

 wliich is kept in proper shape by an external force, that of the 

 muscular fibres that are attached to the bottom of the suckers. If 

 these muscular fibres rekix, the wall of the sucker becomes flattened 

 out by virtue of its elasticity and applied to its substratum, the 

 body-surface of the host ; if now the muscular fibres contract, the 

 sucker assumes the form of a bag, and thus a vacuum tends to 

 form witliin, i2-ivino: rise to a suctorial action. In favour of this 

 view it may be mentioned in addition that in many section's of the 

 suckers the prismatic filjres are seen to be much pressed against one 

 another at the inner side of the suckers near the point where the wall 

 is folded on itself — the part where the fibres must necessarily be 



