468 APPENDIX 



they give the eye. These movements are in some respects like those of 

 the human eye. Note the nuclei of the muscles, and the thickening of 

 the latter as they contract. 



The frontal sense-organs on the antennules are conspicuous but of 

 unknown function. It is possible that the antennae bear auditory setae 

 and perhaps touch-hairs. 



Expt. 16. The muscles may be studied in both their aspects, reflex 

 and voluntary. The heart, gut, and eye have shown us examples of the 

 former sort. The first joint or two of the antennae show well the pulley- 

 action of the voluntary muscles in operating the limbs. 



Expt. 17. Embryology. In many specimens may be seen dark-brown 

 cases containing two eggs each, which are intended to persist when all the 

 adults have died either of ice or of drying. These are the "winter eggs." 

 In other females there are from three to eleven embryos crowded in the 

 brood-sac above the alimentary canal. These may be found of every 

 age from the mulberry stage up to the fully formed young daphnias ready 

 to break out of the sac. The brood-sac contains an albuminous fluid 

 which nourishes the young. The eggs begin in groups of four, and part 

 of these break down to nourish the remainder. 



The ovaries and testes are simple paired tubes; the sexes are distinct 

 and males are relatively uncommon. 



Expt. 18. Drug-actions and similar effects might be studied largely 

 on Daphnia with benefit, for here their action on brain, heart, respira- 

 tion, and digestion might be actually observed directly in its details. 



Expt. 19. Finally, allow the animal to dry up on the slide. Observe 

 thus the relative persistence of the organs, and also the optical changes 

 which protoplasm undergoes when its water is decreased. 



Besides the genera mentioned above, the following should usually be 

 found in abundance in the varied aquaria of the Laboratory : Stylonychia, 

 Hydra, Amphileptus, Philodina, and Chetonotus. 



II. CILIARY MOTION. 



Expt. 20. Direction and Speed of Movement Produced. (Apparatus: 

 Frog-board, small cork platform, lead weights (0.5 to 5 gm.), watch, hot 

 normal saline, metric rule.) Pith the frog's brain (see Expt. 35) and 

 fasten the animal well stretched out on its back to the frog-board. Divide 

 the lower jaw longitudinally on the median line and extend the incision 

 through the esophagus. Turn the flaps widely back and fasten them 

 with clips. Place the little cork block on the mucous membrane of the 

 roof of the mouth between the eyes. (A) Measure with watch and rule 

 the speed at which it is carried downward in millimeters per minute. 



(B) Load the cork with weights and determine the limit of load in grams. 



(C) Warm the membrane with hot (60) normal saline solution (NaCl) 

 and compare the two speeds. Make ten measurements and average 



