PHYLOGENETIC ARRANGEMENT 167 



in Typhaeus. The presence of additional glands behind the spermidacal glands, 

 and corresponding to the copulatory glands of the Geoscolicidae, is met with in 

 Dichogaster. A good many of these characters, it will be observed, particularly the 

 last, are abo found in the Acanthodrilidae. In fact, it seems to be probable that 

 the Geoscolicidae were given off from the main stem of the Megascolides, before the 

 latter had become differentiated into the three families which now exist. As to 

 the phylogenetic relationships of the different families of Microdrili among themselves, 

 something appears to be clear, but a good deal is dark. I have associated together, 

 and given my reasons for doing so, the Lumbriculidae, Tubificidae, and Naido- 

 morpha. There appears to be a fairly straight line down from the Lumbriculidae, 

 through Phreodrilus and the Tubificidae, to the Naidomorpha ; and there is a gradual 

 change in structure which favours the view that that has been the course taken. 



The Lumbriculidae have the simplified muscular layers of the body-wall found in 

 the forms lying below them, but the setae are all of the Lumbricid pattern, and are 

 not by any means always cleft at the free extremity. They have retained the two 

 pairs of sperm-ducts, and the spermiducal glands are less modified than in the 

 majority of the Tubificidae. In Phreodrilus we get the first stage in the development 

 of capilliform setae and the commencing reduction of one pair of spermducts. In 

 the Tubificidae the bifid form of seta, occasional in the Lumbriculidae, has become 

 definitely established. 



On the other side, it seems to me that the relations between the Lumbriculidae 

 and the Moniligastridae and Phreoryctidae indicate the derivation of the former from 

 a group more akin to the purely terrestrial Oligochaeta. The Moniligastridae and 

 Phreoryctidae seem to be offshoots from the Lumbriculid stem, before the complicated 

 structure of the body-wall necessary to a terrestrial Annelid had been lost. Granting 

 the relationship of all these families, which I have argued above, their relative 

 position seems to me to be that which I have just indicated. 



The question of the relations of the Enchytraeidae is a very difficult one. 

 They are unique among the Microdrili in possessing dorsal pores and salivary 

 glands, the existence of which features recall of course the Megadrili. ' Their aspect 

 and habits are largely those of the earthworms,' remarks Vaillant (6, p. aa6). The 

 considerable number of segments which separate the spermathecae and the testes is 

 another character highly suggestive of the earthworms. 



On the other hand the Enchytraeidae present us with resemblances to the group 

 of worms which lies at the opposite extreme of the Oligochaet series. They offer 

 certain points of similarity to the genus Aeolosoma. These are: (i) pores instead of 

 tubular oviducts; (a) a cardiac body in the dorsal vessel of certain species, of 



