22 THE AMERICAN MONTHLY [Febrnary, 



simplicity, though one sufficiently unlike the green-gland to require an en- 

 tirely new course of procedure. Here again was found a body composed of 

 chambers walled-in in a peculiar manner by a tissue of epithelium cells, 

 forming a mucous lining, opening by ducts which communicate with each 

 other and by a common outlet lead away from the gland. The w^all of the 

 cavities, as in the green-gland, was found to shut out the blood from access 

 to the cavities of the chambers, though abundantly bathed w^ith that fluid. 



But with these likenesses in plan there was found entire unlikeness in de- 

 tail, giving rise to entire dissimilarity of actual shape, both of the liver as a 

 whole and of the individual mucous or epithelium cells of its wall. The 

 details of this unlikeness cannot be rehearsed here, but a careful study of them 

 will well repay the student. Both organs, however, are glands ; that is, or- 

 gans of the animal body, whose work is to remove from the blood, or to 

 make from materials removed from the blood, a product which is called their 

 ' secretion.' This product, if of no further use in the body, ma}- be elimi- 

 nated from the bodv as in the green-gland ; or, if of further use, may be dis- 

 charged in a desirable localitv into some other organ, as the secretion of the 

 liver into the pylorus, to act on the food as it enters the intestine for diges- 

 tion. I have called these organs very simple ones, because they are com- 

 posed of only one kind of tissue for work purposes. An organ less simple 

 than these, but still glandular in both structure and use, is the intestine, the 

 organ I shall next consider. 



2. Preparation of the section. — The location of the organ is not diffi- 

 cult to demonstrate. The central portion of the cephalothorax of the cray- 

 fish is occupied by the large globular stomach, an organ with semi-transparent 

 walls, oval outline tapering posteriori}-, and continuous behind into a globular 

 sac, the pylorus, from which passes backward a long narrow tube. The tube, 

 after bending obliquely upward and backward, runs through the entire length 

 of the abdomen, to terminate in an opening upon the underside of the mid- 

 dle plate of the tail fin. This tube is the intestine. It may be removed ad- 

 vantageously at the same time the liver is taken out for hardening, and 

 will furnish very satisfactorv sections if treated in the same manner with that 

 organ and the green gland.* I am not prepared to assert that this method is 

 the best or only one which would give satisfactory results, and I am aware 

 it is not the only one, but it Js a method which will reveal much, and answers 

 well enough for our present purpose. For the purpose of demonstrating the 

 chief facts in the structure of the intestine, it is necessary to make sections in 

 at least two directions, transverse and longitudinal sections being necessary 

 for the study of the outer coats of the organ. 



3. Gross anatomy. — The gross structure of the intestine is very easily 

 determined, and has been already, in part, anticipated. To study it prop- 

 erly one should kill a fresh live crav-fish by means of chloroform or ether, 

 and, having carefully removed the carapace and abdominal terga, immerse 

 the specimen in a bath of fifty per cent, alcohol, carefully parting the organs 

 so as to separate them, but without tearing. The specimen, after fifteen min- 

 utes, should be transferred to a fresh bath of alcohol, this time of seventy -five 

 per cent.,t and transferred again, after several hours, to alcohol of eighty per 

 cent, or more, if permanent preservation of the anatomical preparation is de- 

 sired. This examination of the intestine will reveal its relation to the other 

 organs, also somewhat, though but little, of its own construction. It is a nearly 

 straight tube, of small diameter, found imbedded among the numerous mus- 

 cles of the abdomen, but entirely independent of them ; it runs under the poly- 



* See vol. viii, page 83 ; also viii, p. 767. 



t In these and all preservations a bulk of fluid equal to at least ten times the bulk of the specimen should be 



used. 



