56 THE EARTH-WORM 



(c) The capsulogenous or spermaducal glands, situated on the ventral surface 



of the 9th, 10th, and 11th segments. 



(d) The openings of the oviducts, on either side of the median line, in the 



14th segment. 



(e) The openings of the vasa deferentia, slit-like apertures with tumid lips, 



on either side of the median line, in the 15th segment. 



3. Make a drawing of the side showing : 



(a) The lateral setae. 



(b) The openings of the spermathecae, situated in the grooves between the 



9th and 10th, and the 10th and 11th segments. 



General Structure. 



Pin the worm down, under water or in salt solution, by inserting a pin 

 through the prestomiiun and one through the last segment so that the dorsal 

 surface is uppermost. Cut along the mid-dorsal line from the 25th to the 1st 

 segment and reflect the body-wall, placing pins obliquely through it on each 

 side. Put a pin through each side of the 13th segment. 



Note the mesenteries or transverse septa dividing the ccelome into a series 

 of compartments. In each segment, except the first three and the last, there 

 is a pair of nephridia, one on either side of the alimentary canal, opening to the 

 exterior by the nephridiopores, which are situated near the ventral chsetse. 



A. The Alimentary System. 



The mouth leads into a short buccal cavity. Following this is a stout 

 muscular pharynx, which extends from about the 3rd to the 6th segment. 

 The pharynx is attached to the body-wall by radiating muscular strands. 

 Succeeding the pharynx is the oesophagus, a straight and narrow tube extending 

 to the 14th segment. There are three pairs of oesophageal pouches or calci- 

 ferous glands, one pair in the 11th and two pairs in the 12th segment. The 

 oesophagus expands into a thin-walled crop in the 15th and 16th segments. 

 The crop is succeeded by the gizzard, with thick muscular walls, which extends 

 to about the 19th segment. Following the gizzard is the long straight intes- 

 tine, which leads back to the anus, the terminal opening at the posterior end of 

 the body. The intestine is surrounded by a layer of " yellow-cells " (coelomic 

 epithelium). 



B. The Vascular System (Principal Blood-vessels). 



The dorsal blood-vessel lies above the alimentary canal and extends along 

 the greater part of its length. Anteriorly it gives rise to smaller blood-vessels, 

 which extend over the dorsal surface of the pharynx. In each of the segments, 

 7 to 11 inclusive, the dorsal vessel gives rise on each side to a smaller vessel, 

 which curves round the oesophagus and leaxis into the sub-intestinal or ventral 

 vessel. These six half-hoop-hke vessels are spoken of as "hearts." The 

 ventral vessel lies between the alimentary canal and the nerve cord, and extends 

 along the course of the nerve cord. It may readily be seen by pushing the 

 alimentary canal to one side. 



Make a drawing to show the alimentary and the vascular systems. 



