300 LABORATORY MANUAL FOR ELEMENTARY ZOOLOGY 



(6) Intestine: From the gizzard the brown thin-walled intestine extends 

 straight posteriorly to the anus. Its brown color is due to peculiar cells, the 

 Morogogue cells, which cover it. Cut open the intestine for a short distance 

 along one side, wash it out and observe a thickening in its median dorsal wall. 

 This thickening, the typhlosole, is a longitudinal infolding of the dorsal wall, 

 apparently for the purpose of increasing the absorbing surface of the intestine, 

 for which function it is still further folded by transverse grooves. 



Draw, showing all parts of the digestive system in relation to the segments, 

 properly numbered. This drawing may be combined with that of the circu- 

 latory system, if desired. 



d) The excretory system (Hegner, pp. 175-76): The excretory system of 

 the earthworm consists of a pair of coiled tubes in each segment (except the 

 first three and the last). Each tube is called a nephridium. The main part 

 of each nephridium consists of a tube coiled transversely in the coelome of the 

 segment and opening to the exterior of that segment by a nephridiopore. The 

 beginning of the coiled tube is situated, however, in the segment anterior to the 

 one where the main structure is located; the tube penetrates the septum and 

 opens into the coelome of the preceding segment by a funnel, called the nephro- 

 stome. The nephridia are readily recognizable as the white loose structures 

 on the sides of the digestive tract. Extend your original incision about one inch 

 backward, this time exactly in the median dorsal line. Open out the wall as 

 before by cutting the septa. Pull out the intestine. Pin out the body wall 

 tightly. Observe with the hand lens the paired nephridia in each segment. By 

 manipulating the septa you should have no difficulty in seeing the tube pene- 

 trating the septum arid ending in the segment in front by the funnel, appearing 

 as a white spot. Cut out a nephridium as completely as possible, mount on a 

 slide in water, and cover. Examine with the low power. Identify the nephro- 

 stome (see Hegner, Fig. 89, p. 176); the thin tube which passes through the 

 septum, and forms the first slender loop of the coiled portion; and the remaining 

 wider loops. 



e) The reproductive system: The dissection of the reproductive system is 

 rather difficult and should be attempted only on large and well-preserved speci- 

 mens. By constant reference to Hegner (Fig. 93, p. 181) and by exercising the 

 utmost care in dissection the student will probably be able to find the parts of 

 the reproductive system. As in Planaria, a complete set of both male and female 

 organs occurs in the earthworm, that is, it is hermaphroditic. 



The right side of your specimen has been preserved intact for this dissection. 

 Remove the intestine carefully from the region of the seminal vesicles (no farther) 

 and study their arrangement. The first pair are rounded sacs projecting forward 

 into the ninth segment above the first pair of seminal receptacles. The second 

 vesicles are more elongated and folded and occupy the eleventh segment. The 

 third vesicles are the largest and are much folded, occupying the twelfth and 



