PRACTICAL ZOOLOGY 37 



Aquarium Study. Watch their movements when 

 walking and swimming ; the various motions of which 

 the legs are capable ; the movements of the antennae, 

 eyes, and swimmerets ; the position of the abdomen ; 

 the manner in which food (a scrap of fresh beef) is held 

 and pieces put into the mouth ; the movements of the 

 jaws ; of the breathing organs ; the position of the eggs, 

 if a female "in berry" can be obtained; the means of 

 offense and defense. 



Structure. With a dead specimen, preferably alco- 

 holic, note the hard covering of the body ; the two 

 regions (cephalothorax and abdomen); the rings or 

 segments of which the latter is composed ; the membra- 

 nous parts between adjacent rings ; the indications of 

 segmentation seen on the under side of the cephalo- 

 thorax; the number and structure of jointed appendages 

 on the abdomen ; the use of each kind ; the number, 

 structure, and use of the locomotor appendages on the 

 cephalothorax; the specialization of each pair for par- 

 ticular functions ; the relation between legs and gills ; 

 the arrangement, structure, and use of the various mouth 

 parts ; the structure of the eyes and " feelers ' ; the ear ; 

 the protection of the gills ; endeavor to make out the 

 fundamental plan of structure which underlies the great 

 diversity of form shown by the various appendages 



(Fig. 54). 



Cut through the shell along each side and remove the 

 upper part, thus exposing the internal organs. Note 

 the large' muscles in the abdomen ; the pericardium 

 and heart with the large artery running backward along 

 the middle line of the large abdominal muscle ; the 

 stomach with the bonelike parts in its walls ; the intes- 

 tine ; the digestive glands ; the esophagus ; the repro- 

 ductive glands ; the "green glands" (in the crayfish); 

 the nerve cord lying below the digestive system ; the 



