Hyatt.] 100 [March 5, 



jeff disputes this opinion, declaring that the ascon had the advan- 

 tage over the lencon or sycon both in the amount of surface 

 covered by the collared cells, and also the ease with which the 

 water was admitted, and gives the thickening of the mesoderm 

 by lateral growth as the immediate cause of the lengthening of 

 the branches. This accounts for their length, but not for ampul- 

 lae which must have been due to the localization of the gastric 

 functions in these sacs when they were primarily developed as 

 diverticula of the central gastric cavity. The thickening of the 

 mesoderm and consequent elongation of the pores into tubes 

 would naturally lead to the extension of the feeding cells towards 

 the periphery along these tubes in the direction of the sources 

 from which the food supply was coming. The dilatation of the 

 branches and their adaptation for the interruption of the currents 

 would follow upon the increased opportunities of the cells near 

 the periphery and in these hollows to seize floating food, even if 

 the form and size of the cells did not of themselves occasion an 

 enlargement at the beginning of such a differentiation. We 

 might thus account fcr the origin of the primitive diverticula as 

 portions of a gastro-vascular system and their outgrowth as due 

 to the prior formation of the tubes, but it seems as if still another 

 cause should be considered as assisting in this process and possi- 

 bly having even greater influence. The single ampullaceous sacs 

 or diverticula being outgrowths or branches of the archenteron 

 would, if not prevented by the thick mesoderm, force out the 

 ectoderm and appear externally even in Sycones and Myxospon- 

 giae. This effect is displayed in the lower Sycones, which have 

 lateral ampullae and a thin mesoderm. Sycetta primitiva (Haeck. 

 Calcisp. pi. 41) and Sycaltis conifera (pi. 45) are species in which 

 the growth of the ampullae carries out the thin walls so that each 

 ampulla appears externally as a mamma-form projection. In the 

 typical Sycones in which the mesoderm thickens these organs are 

 proportionally buried until they are no longer apparent externally. 

 One naturally infers, with Haeckel, that each ampulla was a bud 

 equivalent to a complete Ascon, and that Sycaltis and the like were 

 composed of as many " persons," as there were ampullae in the 

 sponge and, therefore, that even those in which the ampullae were 

 buried would have to be considered as colonies in the same sense. 

 It harmonizes better, however, with the history of the development 



