THE ANATOMY. ALIMENTARY CANAL 57 



In all the remaining families of Oligochaeta there are no recognizable traces of 

 these glands or of anything that can be compared to them ; they are absent in fact 

 in the following: — 



Aeolosomatidae. Phreoryctidae. 



Naidomorpha. Lumbriculidae. 



Tubificidae. Moniligastridae. 



It will be seen that the presence or absence of glands appended to the oesophagus 

 is broadly indicative of an aquatic or a terrestrial life ; it is by no means absolutely 

 so ; for Moniligaster is, so far at any rate as is at present known, a purely 

 terrestrial type, much more so than is the family Eudrilidae of which many members 

 are largely aquatic in habit. 



There appears, however, to be a much closer relation between the presence of 

 calciferous glands and comparatively large size and complex organization. This 

 generalization is trammelled by fewer exceptions. Certain exceptions will at once 

 occur, notably perhaps the smaller species of Benhamia which are among the smallest, 

 if not the smallest, of earthworms ; it must, however, be borne in mind that this genus 

 Benhamia is not typically composed of small-sized species ; on the contrary the 

 average size is large, and some of the biggest earthworms are referable to the genus 

 Benhamia. The smaller genera of a given family have frequently a reduced number 

 of calciferous glands. This is best exemplified by the genera Ocnerodrilus and 

 Pygm,aeodrilus, in which there are but a single pair of these glands ; so too in 

 Kerria among the Acanthodrilidae and Gordiodrilus a genus of somewhat doubtful 

 affinities ; the Geoscolecid Ilyogenia has but one pair of glands, and is withal 

 a small member of its family. In fact it seems that everything points to a decided 

 relation between size and absence or presence of calciferous glands. The relation 

 may be more accurately stated thus: — 



Calciferous glands are absent or reduced in number in genera which are entirely 

 composed of small-sized species. When the entire family contains only small-sized 

 genera calciferous glands are completely absent. 



It has been asserted that the presence or absence of these glands is in accordance 

 with the nature of the food of the worm ; the Limicolae of Clapaeede are, as their 

 name denotes, mainly dwellers in soft mud or among weeds, and thus contrast with 

 the boring earthworms. This view, however, does not seem to me to be consistent 

 with the facts. A greater knowledge of the life habits of the Oligochaeta may perhaps 

 reveal some relation between the two series of facts, but at present this knowledge 

 does not exist. 



I 



