SPONGES 



79 



flagellateil cells (Fig. 61, «)• During larval life the cells become modified 

 in their characters, and a certain number pass into the cavity, which is 

 tilled, as is comraouly the case in sponge larvae, with a coagulable 



Development of Plakina monoloiiha. a, larva ; b, section of the wall of the larva ; c . . flagel- 

 lated cells ; ji, fla;;flla ; ml, coa<;uIum, rejiresenting, proliahly, an albuminous fluid tilling; the 

 larval cavity, aiul containing inimiKrated cells of the flagellatecl epithelium ; c, early pupal stage 

 soon after lixation, the gastral cavity being formed by fission ; (/, section across the furcgning; 

 e, rhagon stage, with pores, flagellated chambers, and osculum ; the latter, not clearly shown 

 in the drawing, is in the slight promontory in the middle of the left siile ; /, rmrt of a section 

 across a full-grown spong>'. The attached basal layer is the hypophare : the spongophare 

 (see below, p. 12(i) is folded to form incurrent and excurrent canals, or, ova (between two of 

 thera a stage in the segmentation is seen) ; W, blastulae. (After F. E. Schulze.) 



(albuminous ?) fluid. The details of the blastogenesis and of tlie 

 metamorphosis remain, however, to be investigated. It is probable that 

 they are, on the whole, similar to what occurs in Oscarella. In Halisarca 

 also the statements are conflicting, and the details of the development are 



