MICRODRILI 375 



epidermis. These are reddish brown in A. quaternarium, bright 

 green in A. variegatum and A. headleyi, in the latter even with a 

 tinge of blue. In the largest species of the genus, A. tenebrarum 

 they are olive green. In A. niveum the spots are colourless, and 

 A. variegatum has colourless droplets mixed with the bright green 

 ones. Fig. 195 shows very well the general appearance of the 

 species of this genus. The body has less fixed outlines than in 

 most worms, and the movement of the creatures is not un- 

 suggestive of a Planarian. As the under side of the prostomium 

 is ciliated, and as the movements of these cilia conduce towards 

 the general movement of the body, the resemblance is intelligible. 

 One species of Aeolosoma, at any rate, has a curious habit which 

 is unique in the Order. At certain times, for some reason at 

 present unknown, the worm secretes a chitinous capsule, inside 

 which it moves about with considerable freedom; these capsules 

 when first observed were mistaken for the cocoons of the worms ; 

 they are really homologous with the viscid secretion which the 

 common earthworm throws off when in too dry soil, and with 

 which it lines the chamber excavated in the earth in which it is 

 lying. The worms of this genus multiply by fission ; sexual 

 reproduction has been but rarely observed. 



FAM. 2. Enchytraeidae. 1 This family consists at present of 

 rather over fifty well-characterised species, which are distributed 

 into eleven genera. It is common in this country and in Europe 

 generally ; it has been met with in Spitzbergen and the extreme 

 north ; it occurs in the American continent from the north to the 

 extreme south ; it is also an inhabitant of New Zealand. The 

 worms of this family are nearly always of small size, sometimes 

 minute ; they never exceed an inch or so in length, and that is a 

 rare occurrence. They are equally at home in water and in soil, some 

 species being common to the two media; a few are marine or littoral 

 in habit, while others are parasitic in vegetable tissues. Like most 

 earthworms, and unlike the majority of aquatic worms, the chaetae 

 are without a bifid termination ; the body- wall, too, is compara- 

 tively thick. The perivisceral fluid is often (as in certain Naids) 

 loaded with elliptical or rounded corpuscles. Resemblances to 

 earthworms rather than to the aquatic families of Oligochaeta 

 are suggested by the long distance which separates the sperma- 



1 Vejdovsky, Monographic der Enchytraeiden, Prag, 1879. Michaelsen, "Synopsis 

 der Enchytraiden," Abh. Ver. Hamburg, xi. 1889, p. 1. 



