2180 Journal of Applied Microscopy 



lowing the first moult, or from about the third to the eighth day after hatching. 

 At this age the exoskeleton is so thin and transparent that the following instruc- 

 tive observations may be made: The movement of the gill-paddle, the pulsation 

 of the heart, its strands of muscle fibers, the points of attachment of the heart 

 to the dorsal wall of the body, the valves of the heart and the entrance of the 

 blood during diastole, and its movement into the arteries at systole, arterial and 

 coelomatic circulation of the blood, muscles of the legs, the stomach, ventral 

 nerve chain and its ganglia in the abdominal somites, and in some animals the 

 gills and other structures. Place the specimens in a watch-glass, with water, 

 five parts, one per cent, solution of chloretone, one part, or more, if needed. 

 For studying the heart, stomach and other organs in the thicker parts of the 



"Mi 'oa 



Fig. 6. — A Native Flea {Daphnia) anesthetized with chloretone and photo- 

 graphed from the screen while the class was studying the pulsations 

 of its heart. 



cephalo-thorax, reflect direct sunlight from the mirror of the microscope 

 through a small aperture in the diaphragm, or through a hole in a card 

 placed on the stage of the microscope under the watch-glass. The beam of sun- 

 light should be of less diameter than the width of the carapace of the animal, 

 otherwise lateral rays may temporarily blind the eye of the observer. 



Daphnia. — This may be taken as an example of the water-fleas. Place the 

 specimens in a watch-glass, or in a hollow-ground slide, with water, five parts, and 

 one per cent, chloretone, one or two parts. The animals become anesthetized 

 quickly, and the degree of anesthesia may be controlled by adding water or 

 chloretone with a pipette. Daphnia is interesting from the fact that its heart 

 has an extremely rapid rate of pulsation, but this is reduced by short treatment 

 in strong or long continued immersion in weak chloretone solutions. 



