148 BULLETIN OF THE 
pass. The boundaries of the epithelial cells extend in this case also 
only to within a short distance of the cuticula ; they cannot ordinarily 
be traced up to it, except, as in the case of the dorsal line, in material 
preserved in Flemming’s mixture. The entire ventral line is separated 
from the body cavity dorsally, and from the muscularis ow both sides, by 
a basement membrane. 
In the adult female the lines do not exceed 8 » in width, and are con- 
sequently difficult to study, but I think the same elements can be seen, 
though not so clearly as in the case of the male. 
Biirger (91, p. 636) believed the collection of long cells at the apex 
of the head to be a part of the dorsal line. I can find no special con- 
nection between the two regions, and no striking similarity in structure. 
The shallow groove which he believed characteristic of the external 
surface of the dorsal line is not present in the living animal. It is 
undoubtedly the effect of collapse, since it is found only in preserved 
specimens. I did not find the large cells which he says occur at regular 
intervals in the dorsal line. Perhaps they are found only in individuals 
of a certain age, or they may be connected with the formation of the 
hairs. Proof of the existence of a columnar epithelium, which he con- 
jectured to be present, has been given above. 
c. Muscular Layer. 
In cross sections of the body the muscular layer presents two sharply 
marked portions, a peripheral, radially striated zone (Plate I. Fig. 11) 
and a deep protoplasmic region. Along the line of union of the two 
lies a double or triple row of thickly crowded nuclei, and in some 
regions, or under certain conditions, other nuclei are found scattered 
through the protoplasmic portion. The relative thickness of the two 
zones varies greatly. In the most of the specimens which I cut they 
were of nearly equal breadth, but in some the protoplasmic zone was 
more than twice as wide as the striated portion, and in other cases not 
half so wide. These conditions are represented somewhat diagram- 
matically in a number of transverse sections (Plate II. Figs. 23 to 26), 
which are taken from different individuals. 
The general meaning of the two zones is at once apparent. The 
striated portion is made up of the contractile fibres of the muscle cells ; 
the protoplasmic area represents the non-differentiated portions of the 
same cells together with certain other elements. I met with indifferent 
success in attempting to make macerations of this region and I am not 
able to affirm definitely what proportion of the protoplasmic zone is 
