Anatomical structure of Âspidogaster conchicolA. 489 



Diaphragm, septum. The peripheral muscle-sheath I have 

 already described. Also, that its two inner layers are reflected in- 

 wards to form the diaphragm, for, as is well seen in sagittal sections, 

 the lower, longitudinal fibres of the septum are in continuity with the 

 longitudinal layer of the neck, and in like manner, the upper trans- 

 verse septal muscles pass over in the same layer with the inner, 

 diagonal muscle-layer of the neck. As the supra-septal part of the 

 body is a direct continuation of the neck, it might appear possible to 

 consider the outer muscle layer and cuticle as having left the ventral 

 wall of the body and become reflected over the foot pari passu 

 with the forward growth of the sucker from the posterior end. The 

 origin of the septum , however , as will be shown later , does not 

 sanction this view. The septum (Fig. 3, 2, 7, 9, 19, 21) is composed 

 of an upper layer of transverse and a lower layer of longitudinal 

 fibres. In transverse sections the lower fibres are exceedingly plain, 

 standing out free from each other. When the animal is expanded 

 laterally they are at a greater distance apart and in a single row, 

 but in cases of compression from side to side they are crowded 

 together, especially towards the centre, and may appear as two rows. 

 They are of great length, and nowhere else in the animal is such a 

 diameter reached. Their course is not always in a straight line, but 

 often they make slow, rounded curves, when not in tension, and seem 

 to give off branches — generally considerably smaller than the main 

 fibre — which run at acute angles and join the neighboring fibres. 

 In forming such a conclusion one needs to be very careful, for often, 



I have also described as myoblasts , occurring in sections. His are 

 only slightly smaller than the parenchyma nuclei, while mine have the 

 following relations: large pale parenchyma nuclei 5 to 8 fx, deeply 

 stained nucleolus 1,5 f^i^ nuclear membrane distinct, between membrane 

 and spot a pale space with indistinct, irregular, minute flakes ; little 

 nuclei 2,6 to 4 fx, distinct membrane , no spot (nucleolus), whole 

 distinctly stained red (carmine) with six or more deeper stained granules. 

 They are commonly to be found just outside the more evident sub- 

 cuticular cells, but occur also between the groups of those cells in 

 places where no muscles are to be found, here and there in the paren- 

 chyma with no muscle fibre in connection. Also in groups in the 

 corner between sucker and side wall of foot which is devoid of muscles. 

 Also numerous among the nuclei of the sucker where there are plainly 

 transitional stages in size, staining and chromatin. The myoblasts 

 show a uniformely stained layer of protoplasm round their nuclei, but 

 that is not recognizable in these small cells. 



