GALLOWAY: NON-SEXUAL RErRODUCTION IN DERO VAGA. 127 



lumen outward, here consists of (1) a layer of ciliated epithelium, in 

 which the free ends of the cells form a wavy contour; (2) scattered sub- 

 epithelial cells lying in the basal portion of this epithelium (Plate 2, Fig. 

 13) ; and (3), surrounding all, a distinct basement membrane. Outside 

 the basement membrane is an investment of connective tissue, occasional 

 muscle fibres, and chlorogogue cells. The pharynx, on the contrary, is a 

 more highly specialized structure. Its wall is seen in cross section 

 (Plate 4, Fig. 18) to consist of a dorsal arched portion with a very thick 

 wall, a nearly flat ventral floor, and much thinner latero-ventral connect- 

 ing regions. The thin latero-ventral portions of the wall may be evagi- 

 nated to form a pair of longitudinal grooves (suL). The flexibility of 

 this region allows considerable variability in the form of the tube, for 

 the floor may be infolded into the arched dorsal portion so as nearly to 

 obliterate the lumen, or it may be depressed until the lumen is nearly 

 circular in cross section. Strongly ciliated, long columnar epithelial cells 

 form the dorsal wall, and extend ventrally somewhat more than half way 

 down the sides (Fig. 18, phy. d.). The ventral floor {phy. v.) is similarly 

 formed of ciliated cells, but these are not so long as those of the dorsal 

 wall, while the wall of the groove is formed of cubical non-ciliated epithe- 

 lial cells. The new pharynx, formed as it is during budding, is derived 

 exclusively from material lying anterior to the dissepiment which origi- 

 nally marks the posterior boundary of the budding zone. This shows 

 that it must be either a modification of the posterior half of the intestine 

 of the segment which is involved in the budding process, or a new struc- 

 ture, the material for w^hich is supplied from other growth centres within 

 the half-segment. 



In a budding worm, while the body wall of the bud zone increases in 

 length by the rapid multiplication of the elements making up that wall, 

 there seems to be no corresponding growth on the part of the cells of the 

 intestine. The digestive tube is thus mechanically stretched ; this tends 

 to obliterate the inequalities of its calibre. (Compare Fig. 5 with 

 Fig. 16.) By the continuation of this stretching, the individual cells 

 are transformed from their original columnar character into relatively 

 thin pavement-like elements. I have no evidence that these ciliated 

 epithelial cells divide during the budding process. 



The first signs of cellular activity in the entoderm are seen in the 

 small, indifferent, sub-epithelial cells (Plate 2, Fig. 13). These become 

 more and more numerous, first in the ventral part of the gut, and later 

 in its lateral and dorsal walls ; they form at length a sheath of cells 

 around the epithelial layer which extends through the larger part of the 



