108 OLIGOCHAETA 



that gland-cells ai-e developed in connexion with it just as gland-cells frequently 

 underlie the epidermis. 



This form of atrium is found with but slight modifications in the majority of 

 the genera of Tubificidae (woodcut, fig. 37) ; Ilyodrilus (woodcut, fig. 38) has, 

 however, an atrium precisely similar to that of the Naidomorpha ; in Bothrio- 

 neuron and in Branchiura the atrium is rather difierent, and the state of affairs 

 characteristic of these two genera suggests another interpretation of the morphology 

 of the parts in Tubifex; in both these last mentioned Tubificidae (woodcut, fig. 29) 

 the vas deferens widens out into a terminal chamber which appears to be the 

 atrium ; but this is provided with a single lateral diverticulum (fig. 29, 2), very much 

 larger in Branchiura than in Bothrioneuron ; in Branchiura the lateral chamber 

 has precisely the structure of the atrium in the Lumbriculidae. It is joined by the 

 sperm-duct just where it passes into the muscular atrium ; there can be no doubt in 

 my opinion of the relationship between Branchiura and Tubifex; hence we should 

 expect to be able to furnish a comparison of the different parts of the efferent ducts 

 in each ; two views seem to be possible ; either we must simply consider that the 

 sperm-duct has come to open into the atrium some way from its extremity, or we 

 must regard the sac-like appendix as the equivalent of the prostate of the typical 

 Tubificidae ; in this event the solid character of the prostate in the latter will be 

 a secondary matter ; Stolc (3) is apparently of opinion that the small lateral 

 caecum attached to the atrium of Bothrioneuron (called 'paratrium' by Vejdovsky) 

 is the homologue of the prostate of other Tubificidae, as he indicates both by the 

 same letters in his plates. 



The genus Tdmatoclrilus has an 'atrium' which is intermediate in character 

 between that of Tubifex or Psammoryctes and the more typical Tubificidae on the 

 one hand, and Branchiura and the Lumbriculidae on the other: in that genus 

 EiSEN described and illustrated the presence of a series of separate 'prostates' 

 opening at intervals through gaps of the proper walls of the 'atrium' into its 

 interior ; if these separate masses of glandular cells were combined into a continuous 

 glandular structure we should have an 'atrium' exactly like that of Lumbriculidae, 

 except for the absence of muscles. 



In the Megascolicidae the corresponding organ is constructed upon one or other 

 of two types. In Acanthodrilus, for example, it is a tubular structure of varying 

 length, occupying more or fewer segments, coiled or straight, which is divisible 

 into two regions ; the part of the tube which leads to the exterior is of less 

 calibre and has generally a glittering appearance; this region serves as a duct 

 for the glandular secretion of the distal region; if is lined by a single layer of 



