282 THE AMERICAN MONTHLY [December, 



to finally open at the vent or anus at the tip of the abdomen. The 

 alimentary system is thus a tube passing through the cavity of the 

 body, having connected with and opening into it numerous other 

 organs which are hollow but closed also to the body cavity. There- 

 fore, substances eaten and swallowed being still in the tube are 

 not in a position to reach and afiect many of the organs of the 

 body. To do this they must first pass into solution, and some of 

 them undergo chemical change which enables them to pass or 

 dialyze through the wall of the alimentary tube and thus reach 

 the body cavity, whence they can go to the various organs. The 

 salivary glands, the hepatic cocca, and to some extent the wall of 

 the alimentary tube itself, have the power of producing fluids which 

 when mixed with the food dissolve and alter it so that it can 

 dialyze, this process being called digestion of the food. Some 

 parts of the food are indigestible ; they pass on as fcvces into the 

 colon and rectum to be discharged at the vent. 



2. The circulatory systefn (Fig. 5) in the grasshopper is com- 

 paratively simple, as it is in all insects. It consists of a tube, the 

 iieart, with muscular pulsating wall, lying in the body cavity di- 

 rectly under the terga of the abdomen. The tube is closed behind, 

 but open in front into an artery which passes forward to the head, 

 where the brain lies. The sides of the heart have openings, ostia, 

 a pair in each somite, which admit blood from the body cavity, 

 and, the openings being furnished with valves, the blood is re- 

 tained and pushed forward by the rhythmic pulsations of the heart. 

 There are no capillaries or veins in this circulatory system, and 

 hence only an incomplete circulation results (compare Verte- 

 brata). 



( To be coutiuued. ) 



Microscopic Low Powers. 



By FREDERICK W. GRIFFIN, Ph.D., 



BRISTOL, ENGLAND. 



The comparatively few microscopists who work with the low- 

 est powers are doubtless fully aware of the advantages of day- 

 light in their use. Lamplight, however, modified by tinted glasses 

 and plane mirror, gives a glare with transparent objects, which 

 tries the eyes and seriously impairs definition. I find, however, 

 the new " Zeltnow cupro-chromic light-filter," which has proved so 

 valuable with high powers, to be equally useful with the lowest. 

 It gives a pale green field, as reposeful to the eye as daylight it- 

 self, while a blaze of light is tempered down to due working 

 pitch. All fine details, as the rings of delicate tracheae, or the 

 markings of a dotted surface, are shown up with the sharpest defi- 

 nition. Of course, color is mainly obliterated in this monochro- 

 matic ilkunination, the picture being virtually in monotone, like 



