that constitute the mesenchyme of the body. In doing this, however, 

 it will be necessary for us to widen our field of view and take into 

 account the mass of peculiar connective tissue already described around 

 the genital atrium of Microcotijle. Let us compare the suckers, both 

 anterior and posterior, of Microcotyle, Axine, or any other of the genera 

 mentioned at the beginning of this chapter, with the hemispherical or 

 elongated sac-like organs which form the wall of the posterior or dorsal 

 part of the genital atrium in Microcotijle sciaence and M. chiri, and we 

 shall at once recognise that both are composed of fibres of the same nature 

 ■^so exactly alike are they both in optical characters and in their reac- 

 tion towards staining fluids. Now any one who cared to peruse the 

 descriptions I have given above of this mass of peculiar connective 

 tissue in different species of Microcotyle, and took the trouble of com- 

 paring the figures of it given in Pis. V & VI would at once see that it 

 is in reality a specially differentiated portion of the general mesenchyma 

 of the body. In Microcotyle fiisiformis (PI. V, fig. 1) and M. caudata 

 (PI. V, fig. 3) it is clearly seen to be nothing but a part of the 

 mesenchyma, which has, however, assumed a somewhat different 

 character from the surrounding portion; in M. elegans (PI. V, fig. 2) 

 and M. sebastis (PL YI, fig. 1) it is more clearly distinguishable 

 from the surrounding part, but its origin is still unmistakable; 

 and finally in M. chiri (PI. V, fig. 4) and M. sciaence (PI. VI, 

 fig. 2) a limiting membrane has been developed around it and has 

 distinctly separated it from the surrounding tissue. In M. chiri, 

 however, the outer membrane is, as already mentioned, not so distinct 

 from the surrounding mesenchyma as in M. sciaence and in the 

 suckers of other species, but reveals a perceptible transition into it; the 

 fibres of the mesenchyma passing into, and forming, the membrane. 

 In this connection it should also be borne in mind that tlie wall of the 

 small suckers at the apex of the caudal appendage in Onchocotyle is 



