galloway: non-sexual reproduction in dero vaga. 129 



tween ectoderm and entodewn being at the base of the inner side of 

 that appendage. 



It is only in the region of the pavilion that the entoderm of the an- 

 terior zooid becomes especially active during budding, but anterior to 

 this the sub-epithelial cells form a more or less continuous layer beneath 

 the ciliated epithelium, in a maimer characteristic of the indifferent 

 preanal zone of the mature worm. As the digestive tube lengthens in 

 the formation of new segments, these sub-epithelial cells, in my opinion, 

 become interpolated between the ciliate cells, and thus help to form the 

 lining of the tube, for I find no evidence that the ciliate cells in this 

 region are undergoing division. 



Summarizing the facts concerning the growth regions in the entoderm, 

 we may distinguish the following in the anterior zooid: (1) the ante- 

 pavilion region, where a single layer of sub-epithelial cells reinforces the 

 digestive cells, the latter not being sloughed ; (2) the pavilion thicken- 

 ing, from which the old entoderm is lost ; and in the posterior zooid, 

 (3) the pharyngeal region, of somewhat irregular shape, surrounding 

 the gut and extending posteriorly to the old dissepiment ; from this 

 region also the original entodermic lining is cast off. Between (2) and 

 (3) is a neutral zone, more extensive dorsally, narrowing below, in which 

 the old layer alone exists. 



I shall deal more fully with this in discussing the mouth. 



The old entoderm in the budding zone does not lose continuity until 

 the zooids separate ; thus there is no functional mouth nor anus until 

 separation. The cells of the original lining of the digestive tract show 

 signs of degeneration long before separation. The cell boundaries become 

 less distinct, the cytoplasm stains more diffusely and less intensely, 

 and vacuoles occur in the cytoplasm. 



c. Mesoderm. 



The general arrangement of muscle fibres is the same in Dero as in 

 other Oligochseta. The circular muscles lie beneath the dermis, and 

 beneath these the longitudinal fibres are grouped in four bands : (1) the 

 dorsal band occupies slightly more than one half the circumference of 

 the body ; (2) the narrow lateral band on either side is perhaps equal to 

 one eighth of the circumference, and is separated by a space from the 

 dorsal muscle ; and (3) the ventral band, which is somewhat broader 

 than the lateral bands, from which it is separated by a space. 



In the formation of the budding zone the lateral bands are little in- 

 terfered with until the zooids separate, when their broken euds become 

 vol. xxxv. — No. 5. 2 



