Contributions to the Anatomy and Histology of Tbalassema neptuni Gaertner. 543 



longitudinal muscular ridge which supports the nerve chord. They 

 make with the circular fibres an angle of 20" to 25". 



The absolute and relative thickness of these three layers varies 

 greatly in different regions of the body. They are thinnest about the 

 middle of the body-length, thicker anteriorly, and thickest posteriorly. 

 The layer of longitudinal muscles is, as one would expect, always the 

 thickest. Here and there between the layers nerves can be seen, 

 especially between the outer circular and the longitudinal layer, 

 where delicate branches are visible in longitudinal sections of the 

 body wall. 



The individual muscle cells are embedded in a nucleated con- 

 nective tissue matrix (Fig. 7 c. ^, c.f.n), which is continuous with the 

 cutis. The latter is in the proboscis only present as an enlarged inter- 

 muscular matrix, since the muscles extend up between the root-like bases 

 of the epidermal cells. This connective tissue matrix is beautifully 

 demonstrated in specimens stained in a watery solution of dahlia. 



The muscle fibres, when isolated by maceration in 20 7o nitric 

 acid, show as a rule a number of little connective tissue fibrillar 

 languets, attached to the outer pellicle ^). I regard these as belonging to 

 the connective tissue matrix, where they may well serve as a means of 

 attachment between the muscle fibres and the surrounding connective 

 tissue, or between the fibres themselves (Fig. 9 Î). They are similar 

 to the structures described by Collin (3, p. 481, fig. 6). I cannot 

 believe that these structures are, as Rohde (13, p. 176) suggests, pro- 

 duced by the tearing of the muscle fibres. They are always attached 

 distinctly to the pellicle, and the fibres on which I have observed 

 them show no trace of being injured. The same structure is often 

 visible in longitudinal sections. The mechanical advantage of such a 

 continuity between the elements of a contractile tissue, in producing 

 a perfectly homogeneous contraction without having fixed points for 

 the insertions of the fibres, is obvious. 



I may here remark that in the intermuscular tissue of the pro- 

 boscis I frequently found encysted Sporozoa. 



In transverse sections the individuals fibres are seen to consist of 

 1) an outer hyaline layer, the sarcolemma, better seen in macerated 



1) BüTSCHLi (2) applies the term Pellicula to the outer boundary 

 of the Alveolarschicht i. e. the sarcolemma. He says, p. 331: 

 "Die äusserste Grenzlamelle dieser Alveolarschicht ist, wie gewöhnlich, 

 stärker färbbar und imponirt auch als etwas dickere Linie ; wir dürften 

 sie daher als Pellicula bezeichnen." 



