1888.] MICKOSCOPICAL JOURNAL. 23 



hedral heart and just beneath the dorsal aorta, which runs back from the heart 

 through the abdomen. From this dorsal aorta many very fine vessels may be 

 seen passing to the intestine, provided the gross dissection is very skilfully per- 

 formed upon a very well-preserved specimen : but the process is made veiy easy 

 bv injecting the dorsal aorta with a colored fluid. The examination of the re- 

 lation between the intestine and the blood system shows the absence of any ve- 

 nous system or any capillary system, the blood escaping from the fine branches 

 of the dorsal aorta into the body cavity, where it wanders at large, unlike the 

 arrangement in some higher animals. The generative system, also the liver, 

 lie near to or in contact v\^ith the intestine anteriorly, but do not communicate 

 directly with it at any point, though the secretion of the liver passing through 

 the pvlorus finds its way thence into the intestine. The nervous system of 

 the abdomen lies beneath the intestine and separate from it. It undoubtedly 

 sends frequent nerves to the intestine, but in just what manner these are dis- 

 tributed is not readily demonstrable. The tube itself may be traced from the 

 pylorus, whence it bends upward, running beneath the heart and backward to 

 the anus. The absence of glands opening into the intestine, glands in any 

 way comparable with the malpighian tubules of insects, is an anatomical feat- 

 ure as noticeable as any other to the general student of zoology. The minute 

 anatom}' of the tube itself — its three coats, the inner, middle, and outer 

 coats, or muscular, sub-mucous, and mucous coats — is easily demonstrated 

 from specimens thus examined, in addition to the items already mentioned ; 

 but this demonstration it is far easier to make upon the sections. 



3. Minute anatomy. — If we pursue the same method of study which 

 was followed in the last chapter in the examination of the liver, we shall first 

 examine with a low power (50 diameters) a cross-section of the intestine. 

 This process will be the best one to be followed, for it will give the observer 

 a picture of the entire section, a bird's-e3'e view, showing him how many 

 and various structures will require separate attention. At first the picture 

 will have but very little meaning for the observer, but he will very soon be 

 able to convince himself that the section is really not so complicated and 

 unintelligible as it at first-sight appears. Such a section is represented by 

 figure I. Examination of the section, with the figure used only as a guide 

 to the section and not as itself the ultimate object of study, reveals a very 

 few different objects, but these repeated a very great many times and re- 

 peated in a very systematic manner. If we ai'e able to separate these various 

 elements and learn in what manner they are combined, we shall have gone 

 very far toward unraveling the tangle at first sight presented. And this is 

 exactly what must be done in the case of every section, what is done auto- 

 matically by the expert observer, and must be learned by the beginner in 

 histological study. In searching for the various elements the observer is met 

 by a difficulty which is, perhaps, more characteristic of studies of living 

 things than of inanimate ones ; I mean the wide limits of individual varia- 

 tion anions: units which all are agreed to call identical in character. This 

 variability is often a source of very great tribulation to the observer, who 

 must learn to see identitv in spite of variations, to search for it and to recog- 

 nize it. If asked, How.'' the answer is ready, namely, by extensive observa- 

 tion and, thereb}', bv the discover}- of the series of varying forms by which 

 the extremes are connected. If these principles are practically applied to 

 the examination of the cross-section of the intestine, attentive observation 

 will show : — 



1. A corrugated band (m. m.), itself, not simple, enclosing a cavity; the 

 line is called the nmcous vic?nbra7ie. 



2. A second band continuous (c. m.) and not corrugated, which runs 

 around the entire section on what seems to be its outer, but is in reality its 

 inner, side ; this is the circular tnuscle layer. 



