289 EXPLANATION OF THE PLATES. 



PLATE IV. REPRODUCTION IN POLYPIFERA AND 



ECHINODEBMATA. 



Fig. 1. Hydra viridis (from Thomson), showing sexual organs 

 of both kinds and of very simple structure ; a spermatic capsule, 

 6 ovarian cyst containing a single ovum (pp. 120-124). 



Fig. 2. Reproductive organs of Campanularia Loveni (from 

 Steenstrup, after Loven). The ovigerous capsule or gonophore 

 is surmounted by two sessile sporosacs or meconidia, a, 6, more 

 complicated in structure, and more approaching to the organiza- 

 tion of free medusoids a immature sporosac containing two 

 ova ; b sporosac discharging the young in the guise of ciliated 

 infusorians (p. 123). 



Fig. 3. Another species of Campanularia, detaching free 

 medusoids (from Desor) a polype-cell, b immature gonophore, 

 c gonophore discharging free medusoids d. 



Fig. 4. Medusoidof 0. gelatinosa (f roin Beneden) a umbrella, 

 b manubrium, c marginal tentacles. (p. 122). 



Fig. 5. Infusorian zooid from the ovum of a Medusa 

 (pp. 120-126). 



Fig. 6. Hydraform phase of a Medusa (Scyphistoma; of 

 Sars Hydra Tuba of Dalzell.) 



Fig. 7. Hydraform stock detaching from its summit a pile of 

 nascent Medusae (from Dalzell). 



Fig. 8. B'ipinnaria or precursory zooid of a starfish (from 

 Miiller) (pp. 85,162). At the upper extremity is seen the 

 rudiment of the starfish. The zooid has a mouth and vent of 

 its own, a, 6, but internally its alimentary canal becomes con- 

 tinuous with that of the Echinoderm. 



Fig. 9. Plutens or precursory zooid of an Ophiura (from 

 Mliller) at a is seen the rudiment of the young Echinoderm, 

 with a distinct mouth of its own in the centre of the disc. 



