86 INVERTEBRATE ZOOLOGY. 



elitelluni ; what segments does the clitelham inchide ? Posterior to this the 

 segments vary in number. Notice iii^on the ventral side, anterior to the cli- 

 teUuni, a pair of slit-like openings, surrounded by fleshy lips. These are the 

 external openings of the imsa deferentia. Upon what segment are these ? Look 

 for a pair of minute openings upon the segment just anterior to this. These 

 are the openings of the oviducts, and are visible onl}' during the period of 

 oviposition. Between the 9th and 10th, and between the 10th and 11th seg- 

 ments, are two pairs of minute openings leading into sperniathecae, or recep- 

 tacles for the spermatic fluid. These are visible only during the pairing sea- 

 son. Each segment possesses a pair of nephridia, which open on the ventral 

 side, at the anterior border of each segment, in front of the little pits for the 

 bristles. These are at all times difficult to see. The anus is at the posterior 

 extremity of the body. 



(b) Internal anatomy. The dissection should be under alcohol in a glass 

 dissecting pan, as in the case of Type XVIII. The animal may be cut in two 

 about 10-15 segments posterior to the clitellum. and only the anterior portion 

 studied, as the posterior segments are all alike. An incision should be made 

 with the scissors along the mid-dorsal line, and the animal carefully pinned 

 out. The segments are separated by connective tissue partitions-, the dissepi- 

 ments, which are attached to the integument. These prevent one from spread- 

 ing of the body- walls properly, and should be cut from the integument with 

 a scalpel. When this is done, make a superficial examination of the organs in 

 situ, without farther dissection. Notice: — The alimentary canal with its 

 divisions, running through the center. — The dorsal blood ■vessel, lying iipon it, 

 filled with red blood — a series of 5-6 pairs of enlarged lateral blood vessels, 

 the so-called " hearts," also red. which are given off from the dorsal vessel. — 

 Between these, 2-3 pairs of little orange bodies, the calciferons or oesophageal 

 glands. — The spermatic vesicle, a large mass of whitish lobes, three on each 

 side. — The spermothecae, two pairs of little round sacs, just anterior to the 

 testes and lying on the ventral wall. — The brain, or supra-oesophageal gang- 

 lion, a dumb-bell shaped whitish mass at the extreme anterior end, and lying 

 upon the anterior enlargement of the alimentary canal. — The nephridia, little 

 coiled tubes lying on the sides of the body, in each segment. These are best 

 seen in the posterior portion. Notice farther that the dissepiments are com- 

 plete partitions, dividing the segments into separate coeloms, and allowing 

 continuoiTS organs, as the alimentary canal, to perforate them, as in the dia- 

 phragm of mammals. 



After this general survey, the systems are to be carefiilly dissected, one at 

 a time, cutting merely the connective tissue connections, studying the shape 



