56 OLIGOCHAETA 



' Glands of Morren,' ' Oesophageal glands,' ' Calciferous glands,' etc. The oesophagus 

 in the higher Oligochaeta is usually divisible into two tracts, of which one is more 

 richly supplied with blood-vessels than the other and has a more folded lining 

 epithelium. Frequently this part of the oesophagus is constricted by the septa, and 

 the sections of the tube which lie between the septa are broader than those which 

 are nipped by the septa ; hence a moniliform appearance often exists. This is the 

 case for example in the genus Perichaeta (s. s.). The specialization of a tract of 

 oesophagus having these characters in a more pronounced fashion is characteristic 

 of the genus Onychochaeta and of other forms ; in the genus mentioned that portion 

 of the oesophagus which occupies segments xii. to xv. is wider than elsewhere 

 and is provided with markedly regular and deep folds of epithelium ; this is 

 a step in advance towards the existence of distinct diverticula of the oesophagus 

 such as exist in a great many genera and species ; it is at the same time 

 merely an exaggeration of the vascular tract of oesophagus commonly found in 

 the higher Oligochaeta whether they possess or do not possess distinct calciferous 

 glands. 



In Octochaetus multiporus the oesophagus is swollen in segment xvii. ; in transverse 



ft 



sections of these swellings they are seen to be really diverticula of the oesophagus 

 opening into it by wide apertures on either side. In Pontoscolex the three pairs of 

 calciferous glands first investigated by Pereier are only attached to the oesophagus 

 by their duct on either side ; they are otherwise quite separate from it ; every stage 

 in fact appears to exist between mere dilatations of the oesophagus and diverticula 

 of it ; in the most differentiated form of the calciferous glands, such as are found 

 for example in Pontoscolex, the pouch communicates with the gut by a distinct duct 

 whose walls are lined by cells different in character from those which line the gland ; 

 it is commonly the case that this duct has a lining of ciliated cells while the cells of 

 the gland itself are not ciliated. 



We shall return to a more detailed description of the minute structure of these 

 glands later ; at present we are concerned with their distribution in the group. 

 Calciferous glands in some form or other have been found in the following families ; 

 those families in which they are nearly or quite universal are printed in capitals ; 

 those in which a good many forms are without such glands are printed in clarendon ; 

 finally, italics denote that the glands are rarely met with in the family. 



LUMBEICIDAE. Cryptodrilidae. 



GEOSCOLICIDAE. Perichaetidae. 



ACANTHODEILIDAE. EudriUdae. 



Enckyt7^aeidae. 



