THE ANATOMY. S PE R M I DUCAL GLANDS 115 



the Geoscolicidae. No other genus of Megascolicidae, so far as I am aware, shows 

 the same terminal sac ; this fact is not without its importance ; it is so far an 

 indication that the Perichaetidae, having preserved this structure, are nearer to the 

 Geoscolicidae and the Eudrilidae in which it is better developed than any other 

 sub-family of the MegascoUcidae. I use this as an argument in favour of the low 

 position of the Perichaetidae in the series (see below). 



Another reason which led KosA to dissociate the 'pseudo-prostate' of the 

 Geoscolicidae from the 'prostate' of other earthworms was the existence of special 

 retractor muscles in the former. These, however, are not absent from the latter. 

 In the genus Octochaetus, for example, there are numerous bands of muscular tissue 

 which are inserted on to the bodj'-wall in the immediate neighbourhood of the 

 male pores. A better example still is afforded by two species of Eudriloides (see 

 Beddaed 84), where there is a complex system of retractor and protractor muscles 

 attached to the ducts of the glands themselves. 



It may be useful to tabulate the principal varieties of the spermiducal glands 

 which are illustrated in the accompanying diagram (woodcut, fig. 31). 



A. Glands with a double lining of cells. 



a. Tubular, e.g. Acanthodrilus. 



b. Racemose glands in which lumen has become branched and outer glandular 



layer of cells disposed in discrete tufts instead of forming a continuous 

 layer. 



e. g. Perichaeta. 

 A'. Tubular glands with a double lining of cells covered externally by a layer of 

 muscles ; terminal extremitj' modified into a copulatory apparatus, 

 e.g. Eudrilus, Kynotus. 



B. a. Spherical or more elongated glands with two layers of cells separated by 

 a muscular layer. 



e.g. Rhynchdmis, Moniligaster, Branchiura. 

 b. Outer layer of cells grouped into separate masses. 



e. g. Sutroa, Telmatodrilus, Tubifex (one mass only present). 



C. Tubular glands with single lining of cells. 



e. s- Ocnerodrilus, Kerria. 

 The structui-e which is here termed spermiducal gland has been called 'prostate' 

 and 'atrium' by several; the distinction of terms implies a difference in homology 

 between the different appendages of the sperm-duct, which aa-e by all called ' atrium ' 

 in the aquatic Oligochaeta. Does this difference really exist, or are all the glandular 

 sacs at the end of the sperm-duct homologous throughout the Oligochaeta? I myself 



Q 3 



