44 * JOURNAL OF THE 



Plakina jnonolopha^ the various coeiiogenetic modifications 

 which appear in other sponges may be classified as fi^llows: 



1. The efferent canal system, instead of arising as a 

 single cavity which throws out diverticula, may be formed 

 as so many distinct cavities, - which subsequently unite 

 {Esperella^ Tedania^ Esperia lorenzi and lingua^ Halisarca 

 Diija rdin ii\ Myxilld) . 



2. The flagellated chambers, instead of arising as endo- 

 dermic diverticula, may be formed from groups of mesoderm 

 cells {Esperella^ Tedania^ Chaliniila fertilis^ Myxilla and 

 probably in Esperia lorenzi and E. lingua). 



3. The afferent canals, including the subdermal cavities, 

 instead of being formed as invaginations from the ectoderm, 

 arise as lacunae in the mes-entoderm {Esperella^ Tedania^ 

 Esperia lorenzi ^lw^ lingua^ Stelletta^ Myxilla). In Reniera 

 filigrana they are formed as entodermic diverticula. 



The coenogenetic development of the flagellated cham- 

 bers and efferent canals suggests, as I have said, an 

 essential similarity of nature in the so-called entoderm and 

 mesoderm of sponges. This belief, so long upheld by 

 Metschnikoflf, derives some of its strongest support from 

 this author's physiological investigations (see ante^ p. 10), 

 as well as from the fact first emphasized by Metschnikoff" 

 and Barrois, that in the most common sponge larva, /. <?. , 

 the solid larva, the mesoderm and entoderm form a single 

 indivisible layer. 



And likewise the development of the afferent system of 

 canals in some sponges from the ectoderm, in others from 

 the mes-entoderm, may possibly be taken as meaning that 

 even these two primary layers (the outer and the inner) are 

 not distinctly differentiated from each other in the sponges, 

 or, in other words, that the mes-entoderm is still enough 

 like the ectoderm to form organs ordinarily produced by 

 the latter laver. 



