PHYLUM ANNELIDA 101 



part of the thirteenth segments. The three pairs are united by median masses 

 located in the tenth and eleventh segments. Locate the fifteenth segment and 

 stick a pin into it as a landmark. Gently press the vesicles and intestine to the 

 left and pull off the nephridia from the right ventral body wall by grasping their 

 free ends. Stretch out the right ventral wall tightly. Locate on it the ventral 

 edge of the dorsal longitudinal muscle band, extending as a longitudinal line. 

 Within and in contact with this will be found the lateral setae, projecting inward 

 as minute white elevations, with a slender muscle band between the two members 

 of the pair. One-third of the way between the row of setae and the ventral 

 nerve cord find a white line extending from the middle of the fifteenth segment 

 forward to the tenth. This is the vas deferens or male duct. Examine the septum 

 between the fourteenth and thirteenth segments. The white object in it is the 

 oviduct with a slender tube extending into the fourteenth segment. Then examine 

 the septum between the twelfth and thirteenth segments. A minute white body, 

 the ovary, will be found attached to it. The attached end is the broadest; the 

 free slender pointed end projects backward into the thirteenth segment. If 

 you are in any doubt that you have the ovary, remove it and examine it with 

 the microscope, and the presence of round eggs, the largest of which are in the 

 pointed extremity, will settle the matter. Next look in the twelfth segment 

 for a slender branch extending from the vas deferens over to the fused median 

 portion of the seminal vesicles. Dissect off the roof of the median portion of 

 the seminal vesicle in the eleventh segment and note within its cavity the greatly 

 folded seminal funnel. Anterior to this, attached to the septum between the 

 tenth and eleventh segments, will be found by cautiously picking away the 

 bases of the seminal vesicles a small but distinct round body, the testis. Repeat 

 the directions in the three preceding sentences in the eleventh and tenth segments, 

 and find the anterior branch of the vas deferens, the anterior seminal funnel, and 

 the anterior pair of testes. The mother-cells of the sperm are produced in the 

 testes and set free at an early stage into the seminal vesicles, in which they develop 

 into sperm. Take out a small piece of the seminal funnel, put on a slide in a 

 drop of water, cover, and mash by pressing on the cover glass with the finger 

 and rotating it. Examine with the high power and note the myriads of slender- 

 tailed spermatozoa. The two rounded seminal receptacles in the ninth and tenth 

 segments were previously noted. They receive the sperm from another animal 

 during copulation and are therefore parts of the female system. 

 Draw the reproductive system. 



/) The nervous system: Remove the digestive system as far forward as the 

 pharynx (Hegner, pp. 176-80). The ventral nerve cord, a white cord in the 

 median ventral line, has already been identified. Clean away all tissue conceal- 

 ing it. Examine it with a hand lens and note the enlargements or ganglia which 

 re present in the cord in the middle of each segment and the lateral branches 

 rhich arise from it. Cord and ganglia are really double, formed by the median 



