mm, -^^^^^^f 



;;--::-.:aVv.,. 



i'.i 



■ T.;.'-- 



.<'■'■ .-.'v'i 



Fig. 10. — Diagram of the development of the canal system in various sponges. 

 The ectoderm is indicated by a continuous, and the entoderm by a broken, line. 

 The collar epithelium of the entoderm is expressed by perpendicular striation«. 

 A, cross section through a part of the wall of an ascon ; B, cross section through 

 the wall of a sycon ; 0, cross section through the wall of Leucilla connexiva (after 

 Polejaeff) ; D, vertical section through Oscarella ; a, spaces of the inhalent 

 canal system; b, spaces of the exhalent canal system ; on, osculum. 



