58 OLIGOCHAETA 



A further indication that there is a relation between the glands and the size of 

 the worm where they occur is afforded by the simplification in structure which the 

 glands show in the smaller Oligochaeta. In Ocnerodrilus the lumen of the single 

 pair of glands is but slightly divided up by folds projecting into the lumen ; glands 

 of this worm have been figured by myself and by ErSEN. In Gordiodrilus there 

 is a similar simplicity in the minute anatomy of the single unpaired oesophageal 

 pouch found in the worm. 



The calciferous glands are limited to the oesophagus ; nothing at all resembling 

 them occurs in the intestinal region — except possibly the ' kidney-shaped glands ' of 

 Megascolex coeruleus and of Typhoeus (see below). These latter however are not known 

 to produce calcareous particles such as are secreted by the calciferous glands ; a 

 diflTerence of function which this implies is not of course an objection to a serial 

 homology ; and it is also true that both oesophagus and intestine are derivatives of 

 the mesenteron. It seems however to be clear that the folded structure of the intestinal 

 glands is not comparable to the folded structure of the calciferous glands, for the 

 latter is simply an expression of the fact that the glands in question are diverticula 

 of the already folded lining membrane of the oesophagus, while the epithelium of the 

 intestine is not folded ; hence the complication of the intestinal glands is an independent 

 formation. The calciferous glands vary in number from one to eight pairs ; they are 

 nearly always in consecutive segments, but these segments are not fixed. Thus in 

 Pontoscolex the glands are in segments vi.-viii., while in Benhainiia they occupy 

 segments xiv. xv. xvi. as a rule. It seems that after the first segments of the oesophagus 

 any segment is capable of developing calciferous glands. These organs are not always 

 paired. In the Eudrilidae and in the genus Gordiodrilus there are median unpaired 

 glands which have the structure of calciferous glands ; in Buchholzia there is a median 

 dorsal gland. 



A remarkable fact about the unpaired glands of the Eudrilidae (as seen for example 

 in the genera Eudrilus, Polytoreutus, and Hdiodrilus) is that they coexist with paired 

 glands ; this does not however mean that the two glands are in the same segment, 

 but they are so far independent that there is sometimes a break of a segment 

 between the last unpaired pouch and the single pair of calciferous glands. These 

 unpaired glands of the Eudrilidae were first discovered and described by myself in 

 the genus Eudrilus (62). To these structures Michaelsen has given the name of 

 ' Chylustaschen.' He is of opinion that their function is difi'erent from that of the 

 paired calciferous pouches. The ' Chylustaschen,' according to Michaelsen, are organs 

 not of secretion but of absorption ; by their epithelium nutritive matters are supposed 

 to be taken up from the blood. Here again a difference of function does not by any 



