No. 3-] DEVELOP JIEXT OF MARINE SPONGES. 379 



that of Esperella, the immigration of the ciliated cells does not take place 

 in spots anywhere over the surface, but the inner layer actually overgrows 

 the layer of ciliated cells from the posterior pole forward. In a sectional 

 figure of a metamorphosing larva (PI. XX, Fig. 19) he represents the layer 

 of ciliated cells as overlapped by the inner mass for a considerable distance. 

 I have cut many sections through similar stages, but have never seen a trace 

 of such overlapping. But I can understand how a section through a larva, 

 whose surface had been pitted in on opposite sides, could give rise to such 

 a figure. Such pitting in of the surface may occur when the fixing fluid 

 permits the larva to contract in the moment of death. And I am inclined 

 to believe that the section figured was made through such a larva. 



It is, however, always venturesome to suggest a new interpretation of 

 another's figures. The suggestion is not often happy. This is certainly 

 true of Maas's intimation that my figures of "segmenting" gemmules 

 (Notes on the Development of some Sponges, Journal of Mor- 

 phology, 1 891,) indicate that the bodies in question are not gemmules 

 but eggs, and the " segmentation " is a real segmentation. A glance at the 

 series of figures given in this paper, illustrating the development of the 

 gemmule of Esperella, will show that such an interpretation is impossible. 



The author's renewed study of Spongilla has led him to abandon his 

 former views (for a statement of which see p. 360) on the development of 

 this sponge. He finds that the flagellated chambers and exhalent canals 

 do not arise as diverticula from a central cavity, and that the inhalent 

 canals are not formed as ectodermic invaginations, but that the whole 

 development agrees substantially with that of the marine cornacuspongiae, 

 as described by himself and Delage. My statement, therefore (p. 360), 

 that Maas "brings Spongilla in line with those forms having a rhagon " is 

 interesting only historically. 



On pp. 301 and 36S I cite Maas's observations on the flattening of the 

 ectoderm of the Spongilla larva and its transformation into that of the 

 adult, as a strong argument for the universality of this phenomenon in the 

 sponges. But the author's recent paper makes these citations antiquated, 

 since he now believes that no such transformation takes place. 



Chapel Hill, N.C, June 15, 1S94. 



