13 s. GOTO. 



under consideration. In fact I consider them to be more of an elastic 

 than a contractile nature ; but the reasons for so regarding them will 

 be stated at length further on under the head of general considerations 

 (^I'ide infra, p. 144). 



The surface of the wall of the anterior sucker is covered on all 

 sides by a thin cuticle (PL III, fig. 8). On the side turned towards 

 the mesenchyma, the fibrous connective tissue of the body forms, next 

 to the cuticle, a thin dense layer similar in appearance to the basement 

 membrane already described. 



Each anterior sucker is provided with two muscular bundles, one 

 of which, the larger, is attached to its postero-lateral part and the 

 other, the smaller, to the pontero-median part (PI. Ill, fig. 8). 

 Posteriorly these muscular fibres become mingled with the longi- 

 tudinal fibres of the body. 



The physiology of suction will be considered later on (^cide p. 

 147). 



Posterior siiclers — These are usually very numerous in both Axine 

 and Microcotijle, and in most species of the latter are symmetrically 

 arranged on both sides of the caudal disc, while in the former genus 

 they are always asymmetrically arranged on the two sides in ac- 

 cordance with the general asymmetrical form of the body already 

 described. Their sizes differ in both the genera in different parts of 

 the caudal disc : the i^eneral rule beino: that they are laro-est at the 

 middle of the disc and diminish in size towards the ends. The pos- 

 terior suckers are however mostly smaller than the anterior ones. 



In i)/. reticulata and i)/. sciaenae the suckers are more numerous 

 on the right than on the left side ; and in the latter species the caudal 

 disc is bent at an anu'le towards one side, while in the former the 

 right side presents only a greater curvature. This asymmetry of the 

 body is, as already stated, due to the fact that its one side is longer 



