BY JAS. P. HILL. 
25 
tapers off gradually into the fibrous layer of the epidermis. That 
of the ventral stem is more band-like in form, and laterally passes 
over suddenly into the epidermic fibrous layer. In the cellular 
portion of the dorsal stem gland cells are comparatively few in 
number, while they are altogether wanting in the ventral. Of 
the two stems the ventral is the more strongly developed, and 
towards the posterior end of the body it remains more distinct 
than the dorsal. 
In my preparations, and especially in the ventral cord, the 
" stalked cells " of Spengel can readily be distinguished. They 
are elongated fibre-like cells with generally long deeply staining 
nuclei. These cells are specially developed at the lateral margins 
of the ventral stem. Their fibre-like basal processes traverse the 
fibrous layer, while their outer ends converge towards the middle 
line of the stem, thus enclosing a central space largely occupied by 
the nerve cells. The nuclei of these latter are easily distinguish- 
able by their large size and rounded appearance; they do not stain 
very deeply, possess distinct nucleoli, and exactly resemble 
the nuclei of the nerve cells in the collar cord. The nerve cells 
lie immediately adjacent to the fibrous layer, and this fibrous 
layer as well of the collar cord as of the trunk nerve stems is to 
be regarded, according to Spengel, as made up of the ramified and 
interlaced processes of these nerve cells. Here, as in the collar- 
cord, I have never succeeded in observing the giant ganglion cells. 
Trunk. 
( 1 ) Branchial region: As in all known species of 
Ptychodera. there is below the epidermis a delicate layer of 
circular muscle fibres, in this species only a single fibre in thick- 
ness. The longitudinal musculature internal to this is strongly 
developed and as in the described species is interrupted dorsally 
and ventrally by the vessel stems. The longitudinal musculature 
of the outer wall of the genital wings is considerably stronger 
than that of the inner wall. The latter is interrupted in the 
region of the sub-median lines in whose course the openings of 
the ducts of the gonads are situated. Numerous radial fibres 
