398 THOS. H. MONTGOMERY jr., 
largest (highest) and most numerous at the middle trunk region. 
There is a single layer of muscle cells; but since the muscle cells 
have not a length equal to that of the whole body, the attenuated 
ends of some are to be seen between the enlarged middle portions 
of others. 
Each muscle element is one cell with an axial, greatly elongated, 
cylindrical or ribbon-shaped nucleus, sometimes more or less lobular 
(N Fig. 38, Pl. 39); these nuclei are rich in chromatin and very easily 
demonstrated by suitable stains. Around the nucleus and forming the 
axis of the cell is the non-contractile core, containing a faint-staining 
cytoplasm generally in the form of an irregular network of fine strands 
(Muse Fig. 25, Pl. 38; Figs. 37, 42, Pl. 39): this core seems to ex- 
tend not quite to the attenuated ends of the cell. The periphery of 
the cell is contractile, consisting of longitudinally directed fibrils ar- 
ranged in a single layer. The iron-haematoxylin method enables one 
to determine the finer structure of this part with great accuracy. At 
the attenuated ends of the cell such fibrils are found at all points of 
the periphery, and this is true of their arrangement along the greater 
part of the cell. But at about the middle point of the cell, where 
the nucleus is found, the cell often appears on cross section to be 
bounded by two parallel rows of fibrils, such fibrils being absent on 
the edge of the cell contiguous to the hypodermis as well as on that 
edge next to the body cavity (Fig. 37, Pl. 39). This is generally the 
case with the much flattened cells of the lateral body wall; and at 
these parts of such cells the non-contractile core appears to be un- 
covered by a contractile sheath. It is probably at such points that 
the motor nerves reach the muscle cells from the hypodermis. Though, 
as will be shown later, nerve endings could not be found upun the 
muscles owing to the lack of success in properly differentiating by 
stains the motor nerves, yet the motor nerves probably pass into the 
hypodermis from the nerve cord by way of the neural lamella, since 
the sensory nerves have been demonstrated to take this course. Hence 
the innervation of these muscle elements is most probably from the 
hypodermal side, and not, as in the Nematoda, from their inner sur- 
faces. Possibly intra-vitam staining with methylene blue would finally 
settle this point. 
Cross sections of the muscle cells arranged on the lateral aspect 
of the trunk, show for the contractile zone of each cell the fibrils 
generally quite regular in diameter, arranged in one row on the 
boundary of the cell, and appearing generally small and rounded or 
