Anatomical structure of Aspidogaster conchicola. 4Ô1 



to each side. In the first part of their course they may form a plate- 

 like structure (Fig. 2, 7, 11, 12, 21 PM) on each side bisecting the 

 inferior angle between septum and body wall. From sagittal sections 

 that fall near the sides of the worm it can be seen that these extend 

 from the anterior end of the septum, where they seem to be continuous 

 through the septum with the longitudinal muscles of the neck, obliquely 

 downwards and backwards, or from more posteriorly along the margins 

 of the septum obliquely downwards and forwards to the ventral sucker. 

 Some of these appear to originate in the layer of diagonal muscles 

 of the supra-septal part. When the sucker is fixed the action of 

 these muscles will throw the body backwards or forwards. Horizontal 

 sections between ventral sucker and septum exhibit these fibres in 

 transverse section as small, deeply stained circles filled with a less 

 deeply colored substance (Hohlmuskeln). Across the anterior part of 

 the section these fibres are aggregated into groups, but along the 

 sides just inside of the subcuticular layer of cells they have a necklace- 

 appearance (Fig. 19 PM) on account of the presence of a fine con- 

 necting line between successive circles of the fibres. Certain fibres 

 having a like action come to lie in the same dorsi-ventral plane be- 

 tween parenchyma cells, the sectioned walls of which form the con- 

 necting line of the necklace. Other fibres are dispersed irregularly. 

 Towards the posterior end of the animal muscle-fibres become smaller 

 so that it is often impossible to distinguish them from the walls of 

 parenchyma cells. 



In living animals I have tried to make out the histological structure 

 of muscles (Fig. 26). I have found many with distinct smooth sur- 

 faces, showing a longitudinal fibrillar structure, towards the ends 

 resolving into their individual fibrillae which inserted into the deep 

 staining layer between cuticle and circular muscles. The end twigs 

 show no fibrillar structure. Myoblasts are also present and in fact 

 two sizes of them, or it may be, the few large ones I saw were only 

 exceptional cases. To be sure that these belonged to the muscle-fibres 

 I induced motion, or waited till the animal moved itself, when it was 

 clear that the cell clung to the fibre and followed in its motion. 

 These I have also found in sections even where the fibre showed a 

 considerable length on either side of the myoblast. Most of those 

 found in sections were in the dorsal parenchyma muscles, but some 

 were also in the septum, and belonging to the infra-septal parenchyma 

 muscles. 



In animals that had lain for about 36 hours in a 1 °/o solution 



Zool. Jahrb. IX. Abth. i. Morph, gg 



