MICRODRILI 379 



generative organs, a peculiarity which is shared by Stoic's genus 

 Bothrioneuron. The gills upon the posterior segments of 

 Branchiura sowerbyi and Hesperodrilus branchiatus have been 

 already noticed above (p. 352). A very aberrant genus, perhaps 

 not rightly referable to this family, is Phreodrilus, 1 from New 

 Zealand, first collected in water from a subterranean spring. It 

 differs from all other Tubificids except Hesperodrilus in that the 

 spermathecae lie behind the male pores, a state of affairs which 

 is met with in the Lumbriculidae. Another singularity of 

 structure concerns the sperm -duct, which is wrapped in a thin- 

 walled sac, which has every appearance of being simply the 

 outer muscular wall of the duct. Within this are the compli- 

 cated coils of the duct, and also a quantity of free spermatozoa, 

 whose mode of ingress is difficult to understand. Many of the 

 Tubificidae live in tubes fabricated by themselves, whence the 

 tail end protrudes. The integument in more than one species is 

 vascular. This integumental blood system, universal among the 

 earthworms, appears to be restricted to the present group among 

 the Limicolae of Claparede. 



FAM. 7. Lumbriculidae? This family is not a large one, and 

 is nearly limited in range to Europe and North America ; indeed, 

 if we omit the doubtful Alluroides, entirely to the Palaearctic 

 region. There are only fourteen species, which are referred to 

 eight genera. A number of dubious forms, as is the case with 

 other families, may possibly ultimately swell this list. The type 

 genus of the family, viz. Lumbriculus, upon which Bonnet made 

 his experiments in section and subsequent regeneration, has only 

 within the last year been thoroughly explored anatomically. 

 But all the other genera are well known. The Lumbriculidae 

 are of small or moderate size, and all of them aquatic in habitat. 

 There are three characters which are nearly or quite universal in 

 the genera of the family. In all of them the chaetae are only 

 eight to each segment, arranged in couples, and are either cleft 

 at the extremity or simple. As a rule which has but two excep- 

 tions, the genera Alluroides and Lumbriculus, there are two pairs 

 of sperm-ducts, which, however, communicate with the exterior 

 through a single terminal chamber on each side of the body. 



The dorsal blood-vessel has in the Lumbriculidae a series of 



1 F. E. Beddard, Trans. Roy. Soc. Edin. xxxvi. 1892, p. 273. 



2 Vejdovsky, System u. Morph. d. Oligochacten, ?rag, 1884. 



