SUCTORIAL GROOVES AND MUSCULATURE. 677 



minence which they afterwards attain. They exhibit also in the adult 

 many differences, both in form and size, which are for the most part 

 correlated with the structure of the head. When the latter is broad 

 the suctorial grooves are usually oval or patelliform, but when the 

 head is transversely compressed they appear as longitudinal clefts, 

 limited by projecting lips, and extending more or less deeply in- 

 wards ; often also widened internally, or even continued for some 

 distance backwards into a caecum. 



During life the suctorial grooves are in constant movement, 

 sometimes drawn out, sometimes contracted, according to the changes 

 of form exhibited by the head. The lips, too, open or close according 

 to circumstances. Here and there the head may be seen retracted 

 in the body-mass. 



The Musculature of the head and of the suckers is, however, much 

 simpler than that of the Tseniadas, so simple, in fact, that it can 

 without difficulty be derived from that of the body generally. 1 The 

 greater simplicity lies especially in this, that the cup-shaped muscula- 

 ture, which is so conspicuously characteristic of the suckers of the 

 Tseniadse (and also of the Tetrarhynchi, &c.), is not developed in the 

 forms now under discussion. The muscles which here supply the 

 suckers are integral parts of the general musculature of the body, 

 directly continuous with them, and only differing in their adaptation 

 to specific functions of the attaching apparatus. 



The general musculature differs further from its typical disposition 

 of the Taaniadse in this, that the longitudinal fibres extend in a con- 

 tinuous strand through the whole chain, and do not of course exhibit 

 those metameric interruptions which we have described (p. 293) in 

 those Tcenice which liberate individual proglottides. 



The first modification which these muscles exhibit within the head 

 consists in the loss of that distinction between the cortical and median 

 layers which is so characteristic in the other parts of the body, and 

 especially in the sexually mature joints. Longitudinal and transverse 

 fibres lose their former disposition, and are distributed, becoming at 

 the same time thinner, with some uniformity over the whole internal 

 parenchyma of the head. Even the cellular layer of the subcuticula is 

 abundantly penetrated with fine fibres. This is especially true of the 

 subcuticula of the suckers, which not only exhibits numerous sagittal 

 fibres, but is also penetrated by transverse strands. These continue 

 out to the structureless external cuticle, and pursue a course corre- 



1 See in this connection Sograff's description of the structure of the head of the 

 Bothriocephalidse in the Trans. Friends of nat. hist., Moscow, voL xxiii., part 2, p. 21 

 (Russian), which is, however, incomplete after my investigations which relate especially 

 to B. latus. 



