112 THE AMERICAN MONTHLY [May, 



turns with the freezing weather of late autumn. During these months 

 it is ahnost constantly busy in its round of life-habits, comprised chiefly 

 in foraging for a livelihood and in propagating its kind. 



It goes almost without saying, that next to the frog the cray-fish fur- 

 nishes one of the most important subjects for the zodlogical laboratory 

 in all our inland colleges. Its abundance in most inland waters makes 

 it. easily accessible, and as a type of arthropod, and especially crusta- 

 cean life, few forms, if any, are better suited to elementary work. 



Prof. Huxley, in that admirable book, " The Cray-fish," aptly des- 

 ignates it "An Introduction to the Study of Zoology." And perhaps 

 few subjects have contributed more to the intense interest which cen- 

 tres in tliis science, among beginners, than has this miniature lobster of 

 the fresh waters. 



Prof. S. A. Forbes has also pointed out* the admirable facilities af- 

 forded by the smaller forms of crustacea for the study of the " leading 

 facts of physiology." The minute size and transparency of Asellus or 

 Crangonyx making it comparatively easy to observe " at leisure, under 

 a low power of the microscope, the respiratory movement, the circula- 

 tion of the blood, the motions of ihe heart, and the actions of its valves, 

 the contraction and relaxation of r.uiscular fibre, the process of diges- 

 tion, as well as the general and minute anatomy of the entire animal." 



It may perhaps be worth while to notice in passing that the finest 

 specimens for general laboratorv purposes may be obtained by excur- 

 sions to the smaller streams and flat fields at the " spring thaw, "espec- 

 ially during the usually accompanying period of large rainfall. It is at 

 this time that the larger species of Ca7nbarus^ such ■A't^ gracilis^ obcsus^ 

 etc., which hibernate in the banks and fields adjoining sluggish streams, 

 venture boldly forth for the purposes of foraging, seeking new quarters, 

 or more probably- mating, and may be taken in comparatively large 

 numbers. 



Some of these species grow to large size, measuring in some cases 

 from five to six inches from the tip of the rostrum to the end of the tel- 

 son. With such specimens there is hardly more difficulty in dissecting 

 even the smallest parts than with the lolister ; leaving little to be desired 

 as a fit introduction to arthropod zoology. 



It need hardly be mentioned that they may be easily preserved in 

 alcohol indefinitely, and are therefore easily accessible for laboratory 

 purposes at any time. The only precaution at all necessary is ordinary 

 pains to insure easy access of the preservation to every part. The 

 dense, chitinous walls of the exo-skeleton must be in some way punc- 

 tured to facilitate the process, or otherwise the internal organs will so 

 deteriorate as to be useless for the study of either their gross or micro- 

 scopic anatomy. I have found moreover that those specimens which 

 had been injected in order to facilitate the study of the vascular system, 

 a thing highly important and easily performed, were by far the best pre- 

 served. The injection had apparently greatly facilitated the access of 

 the spirit to the more minute interstices of the tissues, probably by dis- 

 tention of the vessels in part, and in part by setting up an active process 

 of osmosis at once, which extended to every part of the organism. 



Any doubt upon this point may be easily dissipated by the very sim- 



* Bulletin No. i, Illinois Museum of Natural History. 



