ASEXUAL REPRODUCTION IN SAGARTIA 183 



attached to it. Because of this contraction and the conse- 

 quent obUque position of the aboral aperture of the esophagus, 

 the normal edge is often cut in transverse sections of re- 

 generating individuals. The torn lateral edges of the esophagus 

 before their union appear precisely like the normal free edge, 

 and no clear boundary between these edges can be distinguished. 

 Sections therefore show the esophagus open laterally, and it is 

 impossibe to determine, in some cases, whether or not fusion has 

 been completed. Certainly, the union proceeds down the 

 column somewhat in advance of attachment to it of the develop- 

 ing complete mesenteries. 



Formation of new siphonoglyphs 



Following closure of the esophagus, a siphonoglyph appears 

 along the line of fusion of its edges. A siphonoglyph differs 

 from the remainder of the esophagus most obviously in its evenly 

 rounded outline, the other portions showing in sections scallops 

 with their convexities toward the cavity of the tube. A fully 

 developed siphonoglyph shows also, in sections well preserved 

 and stained, more abundant cilia than are to be seen in other 

 regions and usually a more prominent heavy line marking the 

 basal bodies of the cilia In consequence of these distinctive 

 features, siphonoglyphs may usually be readily distinguished 

 from other regions of the esophagus. The time at which differ- 

 entiation of the siphonoglyph becomes clearly evident varies 

 greatly, but is usually about ten days after separation. The 

 undifferentiated esophagus continues to grow laterally on both 

 sides of the new siphonoglyph, leaving the latter permanently 

 in the middle of the regenerated region. 



When division has occurred in the plane of a siphonoglyph, 

 this structure persists and an additional siphonoglyph is formed. 

 Three clear instances of this are recorded as nos. 21a, 21b and 44, 

 the siphonoglyphs being indicated in tables 5 and 6 by the 

 pairs of directive mesenteries with which they are invariably 

 associated. 



