ig8 SCIENCE PROGRESS. 



set of characters which should absolutely separate the two 

 families. Several members of the two families are aquatic ; 

 thus among the Geoscolicicke Bilimba (with which Michaelsen 

 now suggests to unite Horst's A nnadri/us and Glyphidrilus), 

 Criodrilus, whose range the same author has lately ex- 

 tended to South America, Alma and Sparganophilus. Of 

 Lumbricidae Allurus is the only form which is often 

 aquatic. Michaelsen has dwelt upon the fact that all of 

 these, with the exception of Sparganophilus, have the 

 body generally or at least the posterior region markedly 

 quadrangular in outlines with the setae implanted at the 

 four corners. This is an apparent consequence or at least 

 concomitant of aquatic life which is more curious than 

 explicable. So much then for recent modifications of the 

 systematic arrangement of the group. I shall deal finally 

 with various anatomical and histological discoveries which 

 have a general interest unconnected with systematic rela- 

 tions. The most important work under this heading is 

 undoubtedly the recent investigations into the structure of 

 the remarkable family Eudrilidae, a well-defined family 

 whose boundaries have not become in the least indistinct 

 by the discovery of new forms. The family is remarkable 

 on account of its distribution as well as on account of 

 certain anatomical peculiarities. It is limited to tropical 

 Africa — to the Ethiopian region of Sclater, with the sole 

 exception of the type genus Eudrilus, whose ubiquitous- 

 ness, however (America, West Indies, India and the East 

 generally, New Zealand, etc.), makes one suspect direct 

 transference by man. This family is chiefly interesting on 

 the anatomical side by reason of the illustration which it 

 gives of two phenomena, viz., substitution of organs and 

 change in function of organs. 



In all Oligochaeta the ovaries are paired (rarely 

 unpaired) structures which arise from the peritoneal 

 epithelium of the earthworms invariably the thirteenth 

 segment. They are totally unconnected with the oviducts 

 whose open mouths are placed exactly opposite to them. 

 In the Eudrilidae these gonads are enclosed in sacs 

 which communicate with a system of sacs the complexity of 



