SPONGES 



79 



flagellated cells (Fig. 61, ). During larval life the cells become modified 

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

 filled, as is commonly the case in sponge larvae, with a coagulable 



FIG. 61. 



Development of Plakina monolopha. a, larva ; ft, section of the wall of the larva ; , flagel- 

 lated cells ; fl, flagella ; col, coagulum, representing, probably, an albuminous fluid filling the 

 larval cavity, and containing immigrated cells of the flagellated epithelium ; c, early pupal stage 

 soon after fixation, the gastral cavity being formed by fission ; rf, section across the foregoing; 

 e, rhngon 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 side ; /, part of a section 

 across a full-grown spongp. The attached basal layer is the hypophare ; the spongophare 

 (see below, p. 120) is folded to form incurrent and excurrent canals, ov, ova (between two of 

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



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

 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 



