282 ANIMAL BIOLOGY. [Part II. 



On either side of each segment, behind the pharynx, is a 

 coiled tube, nephridium or segmented organ, attached to the pos- 

 terior face of the septum. They are not figured anteriorly, but 

 their position is indicated at s. o. in the last few segments dis- 

 played. The inwardly projecting processes indicated at se. are 

 the sacs of the setce. By removing one of these sacs setae may 

 readily be obtained for microscopic examination. 



From the ninth to the fifteenth segment certain of the genera- 

 tive organs are very conspicuous. There are two globular white 

 sacs on each side, the spermathecce (sp.) ; and there are three 

 pairs of large lobes of the vesiculce seminales (v. s.). Both of these 

 belong to the accessory organs of generation. The essential 

 organs, ovaries, and testes, with their ducts, can only be seen by 

 careful dissection. 



The Body-walls and Septa. Investing the whole body, and 

 turning inwards to line the sheaths of the setae, is a thin trans- 

 parent dense cuticle. This is easily stripped off, especially from 

 a worm that has lain for a short while in spirits. Examined 

 under the microscope it shows intersecting striae, with refringent 

 dots at the points of intersection. Beneath this is a layer 

 generally known as the hypodermis. It contains columnar cells, 

 among which are large oval glandular cells. The glandular cells 

 are very numerous in the clitellum, on the ventral aspect of the 

 eighth to the twelfth rings, at the lips of the male genital pore, 

 and in the prominence on the sixth ring in front of the clitellum. 

 The hypodermis turns inwards at the sheaths of the setae. 

 Beneath the hypodermis is a muscular layer, with circular fibres, 

 between which pigment granules are scattered. Internal to this 

 is a muscular layer with longitudinally-disposed fibres. 



The septa are thin membranes of connective tissue, in which 

 there are radiating and circular muscular fibres. 



The Digestive System. The mouth lies beneath the conical 

 prostomium, the rest of the first ring forming a peristomium. It 

 leads into a buccal cavity, divided by a slight constriction from 

 the muscular pharynx, into which there projects a sucker-like 



