312 OLIGOCHAETA 



seems to be correlated with the aquatic or terrestrial life. There are, it will be. 

 observed, no reasons for inferring that such is the case with the sperm-sacs. 

 I have bracketed together, as being of equal importance, the presence of these glands 

 and the sigmoid character of the setae. It is perfectly true that sigmoid setae 

 are found in all genera of Oligochaeta, excepting only certain Enchytraeids ; but 

 the weight of this fact is partly lessened by the fact that among the aquatic forms 

 there are very generally also capilliform setae, and the sigmoid setae are variously 

 mjodified in shape (e.g. pectinate setae). 



(3) Red blood is only less universally present in the Oligochaeta than sigmoid 

 setae. Apart from the Enchytraeidae, it stops short at the lower Naids, which 

 have very faintly coloured blood; Aeolosoma has colourless blood. One can 

 hardly help inferring from the facts that size is correlated with the colour of the 

 blood ; the minute Oligochaeta have ' white ' blood, the larger and large forms red 

 blood. Now the genus Pachydrilus contains some of the largest Enchytraeids 

 (also, it must be admitted, some of the smallest). 



(4) There remains only the question of the dorsal pores ; I am of opinion that 

 these are distinctly related to the habit of the worm ; thej' are to be found in no 

 aquatic Oligochaeta. The genus Fridericia, in which alone they exist (among the 

 Enchytraeidae), is terrestrial, and found in the driest localities ; so also it is true 

 of many Pachydrilus, &c. But, on the . whole, the group of the Enchytraeidae 

 is, in the matter of its mode of life, in an undecided state ; they are not purely 

 terrestrial nor purely aquatic ; and, if aquatic, neither definitely marine nor fresh 

 water. 



The presence, then, of egg and sperm-sacs, coupled with the sigmoid setae, leads 

 me to place the genus Mesenchytraeus in the position of the nearest approach to the 

 original Enchytraeid. 



I do not, however, think that any other genus can be derived directly from 

 Mesenchytraeus; it is itself too degenerate in the matter of oesophageal glands and 

 the colour of the blood. Nearest to it I should place Buchholzia, Pachydrilus, 

 and Henlea, which have oesophageal glands, and Pachydrilus-like setae ; and the 

 two last will stand nearer to Mesenchytraeus than Pachydrilus, in which all trace 

 of the oesophageal glands has disappeared. Fridericia and Enchytraeus will be still 

 further remote from the primitive stock, and Anachaeta furthest of all. I do not feel 

 able to make any suggestions concerning JDistichopus and Chirodrilus, of whose 

 anatomy we have at present insufficient knowledge. 



The following worms are either certainly or probably Enchytraeids. 



Halodrilm littoralis of Veekill, thought by Vejdovsky (24) to be a Tubificid. 



