HYDRO WS. 



85 



gonotheca, but still remains attached to the blastostyle by a slender peduncle ; this 

 zooid is now seen to be sexual, and contains within the walls of its proboscis, the 

 sexual elements ; 

 the outline is nearly 

 spherical, being cut 

 off at the farther 

 cud where there is 

 an opening into the 

 cavity of the zooid ; 

 about this opening 

 is a wreath of ten- 

 tacles, and pendent 

 ill the cavity of the 

 bell is a proboscis 

 destitute of a 

 mouth ; the cavity 

 of the blastostyle is directlj contin- 

 uous with a central cavity hi this 

 nieconidium, as this kind of zooid is 

 termed, and from this central cavity 

 four radial canals pass out to four 

 equidistant points on the edge or rim 

 of the bell, where they all join a cir- 

 cular canal ; these meconidia never be- 

 come free, but after discharging their 

 contents, they die and disintegrate. 

 The fertilized eggs develop into cili- 

 ated planulas which finally form col- 

 onies of Gonothi/rea Jn/alina. 



These meconidoe which are evi- 

 dently medusa? that never become 

 free, are of great interest, being, in all 

 jirobability, degenerate forms. 



Another large family, the Sertu- 

 LAEiD^, belonging to this same group, 

 is re])resented in America by a beauti- 

 ful species, tSertularia arffentea, so- 

 called from its light silvery color. 

 The colonies are often a foot in height, 

 and the shoots usually grow in clusters; 

 the branches have a subverticillate ar- 

 rangement, giving the colony an arbor- 

 escent appearance. If a small portion 

 of a colony be examined with a magni- 

 fier one discovers very peculiar hydro- 

 tliecas, which are very differently ar- 

 ranged from any described above ; they are nearly tubular, somewhat narrowed at th(^ 

 toj), with pointed lips, and are either free or set into the sides of the stems and branches. 



77. — Gonotheca witb mecomdiaof Gonothyrea: b, blasto- 

 style; (/, conophoi OS 111 various stages of development; 

 <l, meconidia; m, ovum; o, embryos. 



