472 PRANK E. BEDDARD. 



though possibly Microchseta Rap pi may prove to be oue ; 

 at any rate, it is excessively difficult to recognise the setae 

 upon the first few segments ; I have not myself been able 

 to find them at all. They are, however, figured by Benham 

 (11, pi. XV, fig. 1) j but he makes no definite statement as to 

 their presence on the first two or three segments. Leaving 

 Microchseta aside, the absence of setae on the anterior seg- 

 ments is correlated with the entire absence of a prostomium. 

 Not a vestige of this structure could be recognised in either of 

 the two forms mentioned. This correlation, however, is not 

 universal, for Urochseta has no prostomium, and yet the 

 setae are visible, as usual, from Segment 2 onwards. It is 

 furthermore noticeable that in Diachseta Windlei the 

 anterior non-setigerous segments show another modification in 

 the presence of the specialised bundle of transversely running 

 muscular fibres, which I have figured and described as occur- 

 ring in the segments beginning with the 6th. 



In most earthworms the first or peristomial segment is so 

 far unlike the rest that it is grooved longitudinally, and that 

 its epidermis is not clearly distinguishable into two classes of 

 cells, or at least is not so clearly distinguishable as is the epi- 

 dermis of the following segments. Sometimes this modifica- 

 tion appears to affect the 2nd as well as the 1st segment. 



In connection with this modification the varying position 

 of the prostomium may be pointed out. Sometimes the 

 prostomium is attached to the anterior border of Segment 1 ; 

 in other species it encroaches upon this segment, and finally 

 it often completely divides the 1st segment, and reaches the 

 anterior border of the 2nd, 



Earthworms, in moving along, use the mouth as a kind of 

 sucker, even protruding a portion of the buccal cavity; this 

 is remarkably the case with Pericha3ta indica (3), which 

 everts what appears to be the whole of the buccal cavity 

 at each movement. Conversely, there is often a temporary 

 withdrawal of the peristomial segment into the mouth-cavity. 

 These two phenomena appear to have led to the different enu- 

 meration of the segments of Urochaeta adopted by Perrier 



