2 
W. F. R. WELDON. 
means of sections. In the living animal all that can be seen 
is a series of three opacities, one at each end and one in the 
middle of the antero-posterior axis. Of these, the anterior 
indicates the position of the brain (fig. 1, Br .) ; the median 
that of the alimentary tract and reproductive glands ; while 
the posterior is due to the presence of the ductus ejaculatorius 
and vesicula seminalis (fig. 1, V. S.). The relations of these 
various organs can be easily seen in the diagrammatic longi- 
tudinal section (fig. 10). Besides the position of these main 
organs, the presence of large numbers of “yellow cells,” 
scattered irregularly through the tissues, can be seen in entire 
specimens, whether fresh or preserved. 
The body wall is formed dorsally of two, ventrally of three 
layers. In both cases the outer layer is a cuticle (figs. 2, 3, 
4, and 10, Cu.), which again differs in structure on the two 
surfaces of the body. Dorsally it is an apparently structure- 
less or very finely granular layer about 5 yu in thickness, which 
appears in section somewhat ragged at its outer edge, being 
sharply marked off internally from the subjacent tissues. On 
the ventral surface the cuticle (fig. 4) is divided into two 
layers ; an outer, similar in all respects to the whole dorsal 
cuticle, and an inner ( i . cu.), which appears in section as a very 
narrow transversely striated band. Whether this striation 
was due to the existence of fine pores or not could not be 
determined. 
A muscle-layer seems to be present on the ventral 
surface only, and to lie immediately beneath the cuticle. In 
a longitudinal section through the ventral body wall a 
clear space, filled with some feebly - staining homogeneous 
material, is seen to lie in this position, and in this space is a 
row of rounded dots, the cross sections of transverse muscle- 
fibres (fig. 4, m. tr.). In the region of the ductus ejacula- 
torius some of these fibres can be seen passing inwards to form 
part of the sheath of that organ, and here there can be no 
doubt of their muscular nature (fig. 5, m. tr.). Occasionally, 
but very rarely, a nucleus or two can be seen in sections lying 
in the neighbourhood of the transverse fibres, but outside them 
