400 THOS. H. MONTGOMERY jr., 
mid-ventral region of the whole trunk, the ordinary parenchym (Par) 
of the body envelopes the muscle cells. 
In the anterior region of the trunk, a little behind the brain, 
muscle cells radiate from the body wall inward through the large- 
celled parenchym, and terminate in this parenchym layer at varying 
distances from the wall of the stomach (R. Muse Figs. 2, 14, Pl. 37). 
There is thus present here an irregular muscle diaphragm; but its 
structure varies in different individuals; sometimes the muscle fibres 
which compose it come from the lateral aspects of the body wall, in 
others from the dorsal also and even from the ventral (in the latter 
case they pass obliquely upwards around the nerve cord). The function 
of these radial fibres is obviously by their contraction to enlarge the 
cavity of the stomach, making the latter a sucking or pumping organ. 
No other muscle cells were found that those described, thus there 
is no special musculature of the internal organs, and no trace of a 
transverse musculature was found in the body wall. 
B. In the Male. 
The finer structure of the muscle cells is as in the female, and 
the arrangement of the muscular layer is also in general the same, 
except that on the lateral walls of the trunk (Fig. 83, Pl. 42, Figs. 84, 
88, Pl. 43) the cells are flatter and higher, and in the medio-ventral 
line the muscle layer is more deflected upwards around the sides of 
the neural lamella, corresponding to the greater height of the latter 
in the male. Differences are also noticed in the posterior region of 
the body, in accordance with the difference of structure in this region 
in the male. In the tail lobes the muscle cells are largest and most 
numerous dorsally and laterally (Musc Fig. 85, Pl. 43), smaller and 
more scattered on the median side (next the thickened sensory hypo- 
dermis). Only the dorsal and lateral cells extend to the posterior 
ends of the lobes; the contraction of such muscles obviously tends to 
elevate and separate the ends of the tail lobes. The more dorsal of 
the smaller cylindrical cells of the median surface of each lobe extend 
forward as far as the vertical portion of the cloaca, and end in the 
parenchym on the sides of this portion of the cloaca (Muse Fig. 86, 
Pl. 43); their contraction would tend to pull the cloaca backwards. 
The more ventral muscle cells of the median surface of each tail lobe 
extend forwards to form a muscular mantle on the dorsal and median 
surface of each tail nerve, at the plane where the neural lamellae of 
these nerves join with each other at their points of attachment to 
