234 The Microscope. 



are cut so as to show their ends in a cross section. Inside these 

 layers a thin but definite lining covers the skin or body-wall. 

 The thickness of the bodj^-wall can be seen by reference to the 

 scale printed on the figure, to be about one one-hundredth of an 

 inch. The skin is seen further to be similar in all parts of the 

 section. On the back or sides, or below, the levels of the four 

 pairs of setse are shown and certain details of their anatomy 

 may be made out. 



In the centre of the section figure 1, an irregular space defi- 

 nitely bounded can be observed. This space is the cavity of the 

 pharynx, the most anterior organ of the alimentary system. 

 This is bounded everywhere by a wall of vertical elements some- 

 what like those of the ectoderm in appearance. There are no 

 breaks in the continuous wall which they form, not even in the 

 corners (unless some accident of preparation has torn them from 

 their natural position). This layer, the pharyngeal epithelium, 

 is covered by a second layer in the wall of the organ which is 

 muscular tissue used in moving the food contained in the- 

 pharnyx. The pharnyx is held by connective tissue which 

 forms a spongy network reaching across to the body wall on 

 either side. Above the pharynx however there is a space cav the 

 body cavity part of a system of spaces of n^ore importance in 

 other regions of the body. Between the space and the pharynx 

 lies a structure plainly an organ of importance. It is finely 

 granular throughout, and around the margin of its rounded out- 

 line is a zone of rounded bodies. It is the brain, and the 

 rounded bodies are nerve-ganglion cells. The brain is enclosed 

 in a sheath of its own formed by a more compact arrangement 

 of the connective tissue. 



If we compare the section figure 1 with that figured at 2 we 

 shall find that internal anatomy of Lumbriais presents very much 

 more considerable contrasts upon comparison of different re- 

 gions than the great similarity of diff'erent external portions 

 might lead one to expect. Here the body wall is the same as be- 

 fore, presenting cuticle, ectoderm, circular, and longitudinal 

 layers, interruj^ted at the situations of the four pairs of setae. 

 In the centre also the vertical epithelium cells form a skin cover- 

 ing completely the cavity of the pharynx. But the pharynx is 

 plainly divided into two portions one above and one below united 

 by a median portion, and even the low power shows that there is 



