1889.] M1CK0SC0PICAL JOURNAL. 87 



so, although the contents of the stomach seem at times t§ indicate 

 something of the kind. How bits of mussel shell find their way into 

 the maw of these little scavengers it is not easy to understand. It is 

 interesting to watch the munching and grinding which form a part of the 

 eating process. If the crayfish be kept for some time in an aquarium 

 it becomes to a certain extent domesticated, and its habits may be studied. 

 If the aquarium has a transparent bottom the motions of the mouth parts 

 may be well observed. The animal balances itself skilfully on three 

 pairs of legs, while the great claws and the next pair are used to press 

 up to the mouth the desired morsel. The foot jaws work with a 

 combination of a crushing and sawing motion, while the strong man- 

 dibles at each side of the mouth take sharp nips from pieces torn away 

 by the foot jaws. When we remember that in the stomach there is 

 another masticatory apparatus it certainly seems as though these animals 

 were somewhat redundantly supplied. 



I had supposed the crayfish to be principally a nocturnal animal, but 

 its actions in the aquarium are not in accord with that idea. It seems 

 to have no special time for activity, but to be very irregular in its habits. 

 This may be due to the artificial conditions of life. 



The mode of locomotion has passed into a proverb, and every one 

 knows what it means to " crawfish. 7 ' The idea that progression'is ex- 

 clusively retrograde is not true. Four pairs of legs are generally used 

 in locomotion, and they are moved in a definite order, whether the 

 animal moves forward or sideways. Observations on this point have 

 not been close enough to warrant positive statements, but usually 

 the first and third upon one side are moved and immediately after the 

 second and fourth on the other side. I have never observed that they 

 have more than two feet raised at the same time. This of course does 

 not include the large claws, which are not used in locomotion. 



The working of the little pump by which water is made to flow over 

 the gills may be readily observed by cutting away a little notch from the 

 carapace at the point where the cervical suture runs down to the edge 

 of the gill-cover. This causes no apparent inconvenience to the cray- 

 fish, and is certainly not painful. The gill plate is as hard and insen- 

 sitive as the finger nail. The pump is a little scoop-shaped apparatus 

 which is attached to one of the appendages near the mouth, and its 

 working, which may be plainly seen, is a good lesson in animal me- 

 chanics. The gills which this pump supplies with fresh water are objects 

 of much interest to the microscopist, as they exhibit in simple form the 

 essential points of all respiratory structures. 



The egg-laying process is not without its points of interest. The re- 

 productive orifices are double and placed upon the bases of the thora- 

 cic legs. The eggs when extruded are covered with a substance 

 which attaches them very firmly to the fine hairs which fringe the 

 abdominal feet. When the eggs are to be deposited the female curves 

 the tip of the abdomen forward under the thorax. As the eggs pass into 

 the space between the thorax and the under-folded abdomen they are 

 moved about by the motions of the abdominal feet and finally become 

 attached as stated above. The crayfish is very careful of the mass of 

 eggs, guarding it and carefully keeping it out of harm. Thus far no 

 young have hatched in confinement. Strangest of all habits which 

 these lowly animals have is that of changing their clothes. This 



