ELLSHA MITCHELL SCIENTIFIC SOCIETY 



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paragastric cavky at certain points. These evaginations 

 o-ive rise to numerous diverticula of the central cavitv, 

 which constitute efferent canals. The radial chambers are 

 at the same time thrown into groups, each group opening 

 into one of the new diverticula. The intercanals penetrate 

 as before between the several radial chambers, bringing 

 water to the chamber pores, the complexity of their arrange- 

 ment naturally being increased by the folding of the wall 

 of the paragastric cavity. 



The increasing complexity in the Leucon family is 

 brought about by the ramification of the primitively sim- 

 ple efferent canals, the radial tubes growing shorter and 

 becoming in the most complicated types spheroidal cham- 

 bers quite like the flagellated chambers of the non-calcareous 

 sponges. In Lcucilla titer ^ for instance (Polejaeff, PI. VI, 

 fig. 2«), the efferent canals exhibit branching of a simple 

 character. But in such a form as Leucoiiia imdtiforinis 

 (Polejaeff", PI. VI, fig. 3^7) the ramification of the efferent 

 canals becomes exceedingly complex, and the radial tubes 

 here appear as spheroidal flagellated chambers. The inter- 

 canals (or afferent canals, as they are called in all sponges 

 but the Sycons) follow the efferent canals in all their wind- 

 ings, bringing water from the surface pores to the pores in 

 the walls of the flagellated chambers. 



The chief conclusions to be drawn from this anatomical 

 comparison of the various forms of Sycons and Leucons 

 are that the afferent canals of Leucons are homologous with 

 the intercanals of Sycons and are lined with ectoderm; 

 that the flagellated chambers are homologous with the 

 radial tubes; that increasing complexity is brought about by 

 the ramification (or folding of the wall) of the efferent 

 canals. 



The canal system of a complicated Leucon, like Leu- 

 conia, is essentially like that of a common silicious or 

 horny sponge (having flagellated chambers, afferent and 



