TAPE-WORMS OF THE SUB-FAMILY AVFrELLlXlNT.. 35l 



myoblast of A vi tell in a. The longitudinal muscles differ afc 

 first siffht from tlie dorso-ventral and transverse muscles 

 even under a low power, by tlie great development of the 

 muscle-fibres ; the myoblasts themselves are hard to find on 

 account of their great length, which reaches as much as 65 ^t 

 or more, and on account of the length of the muscle-fibres, 

 which can often be followed continuously through more than 

 nine segments. Owing to their elongation, it too frec[nently 

 happens that the myoblasts are not entirely contained in a 

 single section, and owing to the large number of fibres in the 

 longitudinal muscle it is hopeless to look for the continuation 

 of such myoblasts in the next section. 



The muscles are thick, measuring up to 9 /x in diameter, 

 they are i-ound or oval or even polygonal with rounded angles 

 on transverse sections. On thin transverse sections a large 

 number of the muscles, especially those of the outer layers, 

 appear annuliform, having a clear space in the middle. 

 Towards the inner layers of the transverse muscle, all the 

 fibres are found to be solid. Zernecke (1896) figures such 

 annuliform sections of the longitudinal muscles of Ligula, 

 and I have found similar muscles in Dipylidium. The 

 solid muscles are probably derived from tubiform muscles for 

 the following reason. In sections stained with iron-hteina- 

 toxylin, if favourably differentiated, the solid longitudinal 

 muscles are seen to consist of a dark (black) staining core 

 surrounded by a light outer sheath. This peculiarity can be 

 observed in sections passing transversely to the muscles as 

 well as in such running in the direction of the muscle and 

 containing uncut muscles. As we will see later on, the tubi- 

 form muscles contain a portion of the axial mj^oblast in their 

 hollow. If the myoblast deposits or produces the muscle 

 substance, then the centre or axis of the muscle represents 

 the younger deposit, which again stains differently to the 

 outer portion. The fact that the annuliform sections very 

 frequently do not contain any portion of the myoblast is 

 probably due to shrinkage or contraction during fixation. 

 If the solid muscles are the older ones, the outside position 



