MODE OF CONNECTION OF THE JOINTS. 



293 



It is not necessary to enter into details as to the working of the 

 above-described muscles. It is easy to understand that the longi- 

 tudinal iibres shorten the body, while the other muscles give rise to 

 elongation by lessening the diameter. Their action is aided by their 

 general connection with the cuticle, as well as with the surrounding 

 body-parenchyma. We have already emphasised this fact, and also 

 the probable function of the subcuticular cells. 



It is not only the transverse and sagittal fibres which exhibit a 

 connection with the latter. It can also be demonstrated of the longi- 

 tudinal fibres, at least in those cases where the individual joints are 

 sooner or later separated from one another. Then one sees that the 

 longitudinal fibres do not run continuously throughout the whole 

 worm, as in the unsegmented forms and in the anterior imperfectly 

 separated portions of other forms, but pass at the joints into a number 

 of fine threads, by means of which they are inserted into the folds of 

 the constricted cuticle. 



I am most intimately acquainted with the state of matters in 

 Tcenia saginata, in which there is an 

 almost neck-like isthmus connecting two 

 adjacent joints, in itself well marked off 

 from the rest of the body-mass, both histo- 

 logically and otherwise. Especially one is 

 struck with the poverty of the muscula- 

 ture, and with the absence of the spindle- 

 shaped cells, usually placed at right angles 

 to the cuticle. Muscles are not, however, 

 wholly absent. With a high power one can 

 recognise a number, not only of sagittal 

 but also transverse fibres ; both are, how- 

 ever, much sparser, and, the latter espe- 

 cially, markedly thinner than usual. No 

 longitudinal fibres can be detected. They 

 all end near the boundary of the joint, 

 sharply and suddenly, so that there is no 

 doubt that the joints are, thus far at least, 

 independent. The connection between 

 them is effected by spindle cells, which 

 look exactly like those of the subcuticula, 

 except that they are not seated on the 

 cuticle, but are embedded longitudinally 

 in the clear ground mass. Here and there 

 one can plainly see how the fine end of a fibre comes into union 

 with a connectvve-tiss^fgj^^ls^,g^^j§i'^]^]^^ connected by a whole 



Fig. 149. — Longitudinal section 

 of Tcenia saginata, ( x 25.) 



