98 OLIGOCHAETA 



shape than is usually the case; in considering the possibility that Perichaeta is 

 an archaic type of earthworm, the existence of two pairs of egg-sacs is of some 

 importance. Bekgh found nothing in the egg-sacs of the species investigated by 

 him but Psevdonavicellae and darkly pigmented bodies ; he comments upon the fact 

 that the funnel of the oviduct does not open into the interior of the egg-sac as it 

 does in Lumbricus. and suggests on this account that the bodies are functionless. 

 They are certainly not always functionless in this group of earthworms ; I found in 

 Biporochaeta intermedia a pair (one only) of egg-sacs in the usual position which 

 were full of' developing ova, each surrounded by a mass of nutritive cells ; these 

 egg-sacs had no communication with the oviducts, but the fact that they contained 

 so many eggs, both fully mature and developing, seems to dispose of the view that, 

 when there is no connexion with the oviduct, the egg-sacs are without function. 

 In the species just referred to the egg-sacs contained abundant Gregarines which 

 I have also met with in the egg-sacs of Evdrilus; this is another resemblance to 

 the sperm-sacs, where these parasites are invariably to be seen. 



§ 4. Sperm-dv,cts. 



Special conduits for the semen are found in all Oligochaeta, with the sole 

 exception of the genus Aeolosoma. In that worm, according to the recent researches^ 

 of Stolc (1) true sperm-ducts do not exist; the nephridia of all the segments 

 of the body conduct the spermatozoa to the exterior ; this was proved by direct 

 observation ; although the spermatozoa may escape by any of the nephridia (some 

 of the nephridia disappear wholly or in part during the period of sexual maturity), 

 those of the sixth and neighbouring segments especially take upon themselves 

 the function of sperm-ducts, and they are figured by Stolc as rather larger than 

 the others. 



When true sperm-ducts are developed there are never more than two pairs of 

 them^; and frequently only a single pair exist. Each sperm-duct consists of (1) a wide 

 funnel-shaped opening into the coelom and (2) a tube more or less contorted which 

 opens directly on to the exterior or through (3) a terminal chamber, the spermiducal 

 gland, which will be described in the next section. 



Both the funnel and the tube are ciliated throughout. The funnel varies very 

 much in form: In the simpler aquatic forms, and in some of the smaller terrestrial 

 Oligochaeta, it is a flattened plate-shaped disc, with incurved and sometimes also 



' Pereier's statement that there are no sperm-ducts in Anteus requires confirmation. 

 ^ Three have been described in Glyphidrilus weberi; but this is probably a 'sport.' 



