[Hyatt. 102 [March 5, 



with the coelomic sacs of Hydrozoa, Actinozoa and Echinoder- 

 mata, the theory may be of some value to general morphology as 

 an explanation of the appearance of internal antimera, first as 

 irregular and then as more or less regular abortive branches of 

 the archenteron ; their progress in regularity, radial or Asym- 

 metrical, keeping pace with specialization of functions. Thus the 

 process of invagination which begins with the gastrula, when 

 continued causes the archenteron to branch, forming transitions to 

 more complete spongozoons or individuals as in Sycetta and Sycal- 

 tis. The Porifera are not degenerative in any sense, but steadily 

 preserve and differentiate the spongozoon or the primitive ascon 

 type ; through the tendency to a sessile life and the correlative 

 thickening of the mesoderm they have retained the individual- 

 ity of the form as completely as the Dendrocoela among Vermes. 

 The branching of the central cavity is a marked progress in dif- 

 ferentiation by which the outgrowths* or secondary invaginations 

 of the archenteron are converted into essential, specialized organs, 

 the ampullae. Undoubtedly the branching of the archenteron, 

 though not due to true budding, is distinguishable from the bud- 

 ding of an ascon, only by the fact that in the ascon all of the 

 membranes take part in the formation of the new branch or 

 spongozoon, whereas in the formation of an ampulla only the 

 endoderm is the active agent, and when the other membranes take 

 part, as in the Sycetta and Sycaltis mentioned above, no true buds 

 are formed. The Porifera are likely to prove useful, not only in 

 illustrating the primitive relations and origin of organs as diver- 

 ticula, but also in enabling us to see that the morphology of 

 the reproduction of individuals by budding, and of organs by 

 invagination is capable of being followed to a focus where the 

 separation of the two j^rocesses seems difficult both structually 

 and physiologically. 



The large vases Avhich are built up by the growth of the periph- 

 eral parts of a sponge, as in Hircinia campana and all species 

 which construct a general cloaca of this form, are extremely inter- 

 esting in connection with general morphology. No one will dis- 

 pute that these vases are undoubtedly lined by the ectoderm as 

 may be seen by the series of transitional forms, and the color and 

 structure of the internal layer. But we have been obliged to go 

 farther than this and admit that the outer parts of the cloacal 



