THE GONOSOME. r,l 



its summit into a broatl thick disc, which closes, as with a plug, the free end of the gonangiinii. 

 Upon the outer side of this disc a thin chitinous investment is excreted, becoming continuous ui 



Fig. 23. 



Mature female gonangium with marsupial 

 eliamber in Sertularia rosacea. 



a, a, Cavity of the proper gonangium ; 

 c, c, blastostyle ; d, opercular Bumniit of blas- 

 tostyle; e, one of the eye's radiating arms which 

 are given oft" from the summit of the blasto- 

 style, marked by a chitinous sheath /, which is 

 prolonged from the walls of the gonangium ; 

 the arms are seen surrounding the marsupial 

 chamber, which contains ova advancing to- 

 wards the condition of planula?; g, the six 

 shorter spines which ci'owu the marsupium ; 

 h, the two longer lateral spines ; ?, i, the two 

 lateral ridges of the gonangium, wliich are 

 continued into the longer spines; k, k, k, 

 gonophores in various stages of development, 

 all surrounded by the gubern.icular membrane. 



Fig. 24. 



Young female gonangium of Sertularia 

 rosacea, showing the formation of the 

 marsupial chamber. 



a. Cavity of the proper gonangium ; 

 c, blastostyle ; c, radiating arms prolonged 

 from the opercular summit of the blasto- 

 style ; y» chitinous sheath of arms ; i, i, 

 lateral ridge of gonangium ; k, gonophore 

 surrounded by its guberuacular membrane. 



the edge of the disc with the chitinous walls of the gonangium, while in the centre of the disc 

 the chitinous investment is deficient, leaving here the summit of the blastostyle naked. 



The edge of the disc soon becomes produced into eight thick symmetrically radiating lobes {(%t') 

 which gradually elongate themselves, carrying with them a continuation of the chitinous excretion, 

 which forms a wide tube around each ; and now bending upwards, in the form of eight arms 

 with enlarged extremities, they remind one of the disposition of the petals in a flower, and 



