STRUCTURE OF A GENUS OF OLIGOCH^TA. 11 



productive system ; no one will probably find fault with this, as the reproductive system 

 in the Oligochaeta generally is most useful for systematic purposes. 



From the point of view of its reproductive organs, Moniligaster does not agree with 

 any family of Oligochaeta. The clitellum, which has at present only been described in 

 M. sapphirinaoides [Bourne, 6], probably occurs also in other species, though it is very 

 remarkable that none of the examples studied by Perrier, Horst, and myself showed 

 any traces of it. It is possible that the explanation of this is that the worm only 

 develops the clitellum during a very short breeding season, as in many of the 

 Limicoline genera. In any case, the forward position of the clitellum (segments 

 X-XIII, inclusive, in M. sapphirinaoides) is a remarkable point of resemblance to many 

 aquatic genera — e.g., Phreoryctes ; it is quite unlike anything that has been recorded 

 among earthworms. I have already dwelt sufficiently upon the resemblance of the 

 atrium to that of the Lumbriculidae and I may add of Iliodrilus (Stolc, 9, Tab. iii. 

 fig. l) ; the presence of a single vas deferens on either side only occupying a single 

 segment is not met with elsewhere among the Oligochaeta, except in the Naidomorpha. 



The simplicity of the vas deferens funnel is also a point to be noted in this connection. 



The egg sacs are stated by Bourne [6] in M. minutus to " occupy segments 

 XII -XV at least ;" Horst [8] found that in his species M. Houteni, the egg sacs extended 

 through segments XIV-XVI. ( ? XIII-XV). The large size of the egg sacs is clearly an 

 important point of difference from earthworms, where these bodies are so minute as to be 

 often only with great difficulty recognisable. 



Briefly to recapitulate. 



Moniligaster differs from all other earthworms in the following points : — 



1. Clitellum occupies segments X-XIII. 



2. Male pores in intersegmental groove X/XI. 



3. Female pores in intersegmental groove XI/XII (?). 



4. Vas deferens only occupies one segment ; atrium with a glandular investment, 



formed by peritoneal cells. 



5. Ovary in segment XI (?). 



6. Egg sacs occupying a large number of segments, XII-XV (or XIII-XV ?). 



7. Spermatheca with an immensely long duct. 



The structure of the body- wall, septa, alimentary tract, and nephridia is on the whole 

 like that of earthworms, except that there seem to be no calciferous glands. 



The characters of the reproductive organs are such that Moniligaster cannot be referred 

 to any group of Oligochceta, though it agrees in particular points with several families. 

 The clitellum is near that of Phreoryctes, and I believe the Lumbriculidae; with these 

 groups the absence of genital or penial setae is another point of agreement ; the structure 

 of the atrium affines the genus to the Lumbriculidae, but the characters of the vas deferens 

 are more like those of the Naidomorpha. The egg sacs, from their large size, agree with 

 those of many Limicoline families ; but in being paired and the sperm sacs also, the 



