PLATE IX. 



Fig. 1. Young Porpita with the eight primary chambers, surrounded by simple straight vascular canals 

 with eight large primary four-knobbed marginal tentacles t, sixteen secondary tentacles t', 

 of about half the length of tlie first set, and a third set of still smaller tentacles (", from 

 thirty to fifty in number, alternating between them and scarcely projecting beyond the mar- 

 gin of the disk. The disk measures* only jV" in diameter. 

 Fig. 2. A somewhat older stage, the disk measuring about J more in diameter than the preceding 

 stage. The tentacles have greatly increased in length and are proportionally more slender ; 

 the primary and secondary tentacles also have two coils of tentacular knobs. 

 Fig. 3. Still older stage, the primaiy chambers occupy a comparatively smaller area of the disk ; the 

 secondary tentacles, t.', are nearly as long and slender as the eight primary ones, t ; and the 

 third set of tentacles, (", have also developed tentacular knobs. 

 Fig. 4. Ramifications of the vascular system in an older stage than the preceding, in which the eight 

 primary chambers, with their openings n', are now surrounded by irregular circles of open- 

 ings, o", o'", leading to the second and tliird concentric chambers of the disk. 

 Fig. 5. Extremity of the primary tentacle of a young Porpita, in the stage of Fig. 2. 



