ANIMAL BIOLOGY 



le 



FIG. 89. Level length- 

 wise section showing 



k, heart. 

 d, green gland. 

 le, liver. 

 kie, gills. 

 kh, gill cavity. 

 ma, stomach. 



(After Huxley.) 



to the vent, 

 or small? Straight or 

 curved? The powerful 

 flexor muscles of the tail 

 lie in the abdomen below 

 the intestines. Compare 

 the size of these muscles 

 with the extensor muscle 

 above the intestine (Fig. 

 90). Why this difference ? 

 Does the food tube ex- 

 tend into the telson? Lo- 

 cate the vent (Fig. 90) . 



pair of legs in the female, and the fifth 

 pair of legs in the male (Fig. 88). The 

 eggs are carried on the swimmerets. 



Internal Structure. - - SUGGESTIONS. If 

 studied by dissection, it will be necessary 

 to have several crawfish for each pupil, one 

 for gaining general knowledge, and others for 

 studying the systems in detail. Specimens 

 should have lain in alcohol for several days. 



The Food Tube.- -Is the stomach in the 

 head portion of the cephalothorax or in the 

 thoracic portion? (Figs. 88, 89). Is the stomach 

 large or small? What is its general shape? 

 Does the gullet lead upward or backward? 

 Is it long or short? (Fig. 88.) The mid tube, 

 which is the next portion of the food tube, is 

 smaller than the stomach. On each side of 

 it are openings from the bile ducts which 

 bring the secretion from the digestive gland, 

 sometimes called the liver. Does this gland 

 extend the whole length of the thorax? Is 

 it near the floor or the top of the cavity? 

 The third and last portion of the food tube 

 is the intestine. It extends from the thorax 

 Is it large 



FIG. 90. SECTION OF CRAWFISH showing 

 stomach JT, liver //, and vent a. 



