1888.] MICROSCOPICAL JOURNAL. 65 



Elementary histological studies of the Cray-fish. — IX. 



By henry L. OSBORN. 



CHAPTER III. — THE INTESTINE. — {^Continued from page sjj) 



4. Histology. — The beginner will be mistaken if, on first look at the sec- 

 tion, he expects to find each cell of the various tissues standing out for easy 

 recognition. He must very carefully observe the caution we have already 

 recommended in connection with these studies. The cells are so thin-walled 

 that they are pressed into somewhat irregular shapes, and the thin walls often 

 baffle all our attempts to see them. But if he will apply the principle I be- 

 fore insisted on, of picking out the repeated parts and observing them closely, 

 he will find his way through. I am convinced that the faithful study of the 

 sections, with intelligence guided by some such principle, will help any be- 

 ginner to an insight into the real construction of the tissues of his section, and 

 that, without it, while he may be taught, by rote, which is any particular kind 

 of cell, he will never reach a place where he can, without a guide, study with 

 well-founded confidence. 



The intestine is, in one sense, a much simpler organ than the liver, the sub- 

 ject of the last study, for it consists of only one hollow tube of a certain length 

 and diameter, while the liver is formed of a very large number of blind 

 pouches, which are connected with each other and with tlieir ducts in a 

 manner not, at first sight, entirely plain, and only so after considerable study. 

 The anatomy of the intestine is far simpler than that of the liver ; but the 

 histology of the intestine is much more complex than that of any organ thus 

 far reached in the course of these studies. I have already pointed out the 

 existence of several* tissues, the mucous membrane, circular muscle layer, 

 longitudinal muscle layer, and the sub-mucous layer. Nothing similar to 

 these muscular coats can be found in the green gland or in the liver. I shall, 

 later, take occasion to point out that the mucous membrane is similar in all 

 three. In studying more closely than we have already done, it will be con- 

 venient to follow the order already followed in their coarser recognition. 



I. The mucous membrane must be studied with a power of 250 diam. 

 If the section be a good one, both well-preserved and cut thin, the membrane 

 will appear to be a broad tinted band with a ' hyaline ' or transparent zone 

 at one side next the cavity of the intestine and with a thin, sharp line bound- 

 ing the band on the other side, at some places, but entirely disappearing in 

 many others. This broad band will be found to be by no means of even tint, 

 but near the hyaline border in many places will be seen innumerable minute, 

 very dark specks which do not extend entirely across the band, and at about 

 the same distance from the border of the band a row of oval bodies, the 

 nuclei of the cells. By further careful study faint lines maybe seen crossing 

 the band somewhat as shown in figures 2 and 4. After the discovery of these 

 cross-lines, by sufficient study the observer can convince himself that the 

 cross-lines*' bear a certain relation in position to the position of the nuclei, 

 falling one on each side of them, as shown in the very highly magnified 

 camera-lucida drawing, figure 3. These features, though perhaps nowhere 

 readily seen, will in many places be indistinctly seen, and often definitely 

 enough to leave no doubt as to the correctness of the interpretation. The 

 broad band is a corrugated sheet — it is a sheet of substance granular and 

 deeply stained ; scattered through it, at approximately the same level, are 

 bodies, oval in outline, more intensely stained than the granular substance of 

 the sheet. The oval bodies are never at the upper part of the sheet or the 

 part next the cavity of the intestine. The sheet, further, the lining of intes- 



