The Microscope. 233 



to the process of histological preparation, cannot fail of making 

 sections which show all that a section can show. 



The goal of too many has been reached when this point is 

 attained. The section collector however goes through all the 

 drudgery of the desert and never once sets foot upon the promised 

 land. The real purpose of this article is to study sections of 

 Lumhricus to see what they can tell us which we could not see in 

 an anatomical study. Here is a section from a series of successive 

 slices cut the length of the body. This section is about the one 

 hundred and fourth in the series beginning with the front one. 

 It is seen at a glance to consist of three principal parts, the skin, 

 the brain and the alimentary tube. We are examining it with 

 a low power. We are very much tempted to put the high power 

 •on at once to see more clearly some little part which catches our 

 eye, but this temptation must not be followed ; for if it is we 

 shall go on chasing over the section and completing nothing. So 

 we give our attention first to noting the parts before us and try- 

 ing to read from them the structure of Lumbricus. First of all 

 we note a thin translucent boundary line represented by the 

 heavy black line of figure 1, interrupted only at 8 points where 

 "the setae come out through it. This is the cuticle. Just within 

 "the cuticle a distinct layer but of small bodies vertical to the 

 •surface encircles the section. This belt is also interrupted at the 

 ■ setae and can be seen to bend in to form pits which the setae fill. 

 The layer which thus covers the body externally just beneath 

 the cuticle is the ectodermal portion of the skin, the vertical ele- 

 ments barely visible under the lower power are the units or cells 

 the more careful study of which will be better deferred until the 

 general anatomical relations of the section have been fully de- 

 i,ermined under a low power. Directly under the ectoderm a 

 "belt c. mu. parallel with the last is seen. It is composed of ele- 

 ments which are parallel with the surface marked here and there 

 "with elongate deepened spots. This belt is also interrupted at 

 "the positions of the 8 setae, but is otherwise continuous through- 

 out the section. It is the " circular-muscle " layer of the skin, the 

 "fibres of the muscle long and thread-like being wound around 

 and around the body are seen lengthwise in a cross section. 

 Another muscular layer appearing very unlike c. mu. is seen 

 within it forming the inner or longitudinal muscular layer. This 

 is composed of fibres which run lengthwise in the body-wall and 



