54 OLiGOCHAETA 



to be no buccal cavity at all but the mouth leads at once into the pharynx. 

 The latter has usually exceedingly muscular walls, the musculature being dorsal ; the 

 lumen is folded and ciliated, in the lower Oligochaeta, and dorsally, as Benham has 

 lately pointed out in the earthworms — at least in many earthworms. In Pei-ichaeta 

 the buccal cavity is markedly capable of extrusion; to a less extent this is also 

 the case with other Oligochaeta. The pharynx, on the other hand, is not to be 

 exti-uded. After the pharynx comes the oesophagus ; this is a tube of moderate 

 calibre which extends through a varying number of segments. The oesophayus 

 is always ciliated in the lower Oligochaeta but not throughout its whole extent 

 in the earthworms ; the cilia usually begin after the calciferous glands, if these are 

 not present in the hinder region of the tube ; thus in Liiyodrilus the cilia begin in 

 segment xiv. The oesophagus is the most specialized part of the alimentary tract 

 in correspondence with the cephalization exhibited by the other organs which lie 

 in the anterior region of the body. The pharynx is often supplied with glands 

 which have been variously termed ' salivary glands,' ' septal glands ' ; they are not 

 to be confounded with 'salivary glands' of apparently nephridial origin which are 

 treated of under the excretory system. 



The septal glands (at one time mistaken for ganglia of the visceral nervous system) 

 are especially conspicuous in the aquatic Oligochaeta, where they are attached to the 

 septa, whence of course the name ; they are masses of pear-shaped cells, each cell being 

 prolonged to form its own duct ; the ducts appear to enter the pharynx. Vejdovsky 

 has figured very obvious glands of this kind in the embryo Allolohopfwra. 



These septal glands seem to me to be simply epidermic glands which have been 

 invaginated along with the stomodaeum ; they are appended to a part of the alimentary 

 tract which must be, though the actual proof is in most cases wanting, of epidermic 

 origin ; in this case the glands will be entirely comparable to those which open on 

 to the genital papillae of the Perichaetidae, or in fact to the glandular cells of the 

 clitellum. On the other hand their position upon the septa and lying freely within 

 the coelom seems to be against this interpretation, and in favour perhaps of regarding 

 them as homologous with the septal sacs of certain species of Perichaeta and Acantho- 

 drilus referred to above. 



Gizzard. In the majority of the Oligochaeta a part of the oesophagus is modified 

 into an organ which is usually called the gizzard ; this part of the alimentary canal 

 is distinguished by the immensely thickened muscular walls and by the thick chitinous 

 layer secreted by the lining epithelium. As to the muscular layer, it is the circular 

 fibres which are especially increased. The gizzard is absent in a large number of 

 Oligochaeta, particularly among the mud-living forms; in no family of Oligochaeta 



