348 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D. Ser. 



Seven cases were dissected, each in a stage shortly after 

 the division of the mouth. In but one had the mouth 

 divided transversely (fig. 2.) The single siphonoglyph, 

 lying at one end of the mouth, was therefore not included 

 in the division, but remained intact as the siphonoglyph of 

 the larger oesophagus. There was no sign of a siphonoglyph 

 upon the other mouth. 



In each of the other six cases the division plane had 

 passed through the greater axis of the mouth, dividing the 

 siphonoglyph into two portions, one pertaining to each of 

 the two new oesophagi. Figure 3 shows the siphonoglyph 

 dividing, slightly in advance of the division of the oesopha- 

 gus. Figure 3« is toward the aboral end of the oesopha- 

 gus: neither siphonoglyph nor oesophagus has divided. 

 Figure 3$ is a section taken nearer the oral disk; the 

 siphonoglyph here exhibits a median fold marking the line 

 of division, and the oesophagus is constricting longitudinally. 

 A section taken above the point of junction of the two newly 

 formed oesophagi is shown in fig. 3c; the siphonoglyph has 

 divided, and each portion, by the division of the primary 

 pair of directives, possesses but one directive mesentery. 

 The plane of division has passed between the members of 

 pair m, also, so that each oesophagus (3c) obtains one 

 mesentery. 



A similar case is shown in figs. 4« and ^b, which are 

 drawn from a diglyphic polyp with an unusually large num- 

 ber of complete mesenteries. But one siphonoglyph is 

 affected by the division ; so that the smaller derivative 

 oesophagus possesses two siphonoglyphs, the larger, one. 

 The mesenteries of the pair of directives D, and non-direct- 

 ives in are apportioned as in the preceding case. This sep- 

 aration of the members of a pair is characteristic of longi- 

 tudinal fission. 



Somewhat later stages are shown in figs. 5 and 6, in each 

 of which the derivative oesophagi are distinct throughout 

 their length. While the siphonoglyphs in each polyp are 

 entirely separated, they are still closely related in position ; 

 and the directives exhibit the divergence characteristic of 



