144 



ZOOLOGY 



SECT. IV 



Bougainvillea (Fig. 105) is a good example, the cuticle stops short at 

 the bases of the hydranths, and the reproductive zooids are not 

 enclosed in gonothecse. It is for this reason that, in classifications 

 founded on the zoophyte stage, the Anthomedusae are called Gymno- 

 blastea or naked-budded zoophytes (see also Fig. 106, 1, 4, 5). In 

 the Leptomedusae the cuticle is usually of a firmer consistency than 



in the first sub- 

 order, and fur- 

 n i s h e s hydro- 

 thecee for the 

 hydranths and 

 gonothecse for 

 the reproductive 

 zooids : they are 

 hence often 

 classified as 

 Calyptoblastea or 

 covered - budded 

 hydroids. T o 

 this group belong 

 the commonest 

 species of hy- 

 droids found on 

 the sea - shore, 

 and often mis- 

 taken for sea- 

 weeds the 

 ' Sea-firs 5: or 

 Sertularians. 



The medusae 

 also exhibit 

 c h a r a c teristic 

 differences in the 

 two sub - orders. 

 In the Anthome- 

 dusse the um- 

 brella is usually 

 strongly arched, 

 and may even be 

 conical or mitre- 

 shaped (Figs. 105; 

 106, 7 ; 110, 1 and 2) : its walls are thick, owing to a great develop- 

 ment of the gelatinous mesogloea of the ex -umbrella, that of the sub- 

 umbrella remaining thin ; and the velum is considerably wider than 

 in Obelia. But the most important characteristics are the facts that 

 the gonads (gon) are developed on the manubrium and that lithocysts 

 are absent. Sense-organs are, however, present in the form of specks 



105. Bougainvillea ramosa. A, entire colony, natural 

 size ; B, portion of the same magnified ; C, immature medusa. 

 dr. c. circular canal ; CM. cuticle or perisarc ; ent. cav. enteric 

 cavity ; \hyd. polype or hydrauth ; hyp. hypostome or manu- 

 brium ; med. medusa ; mnb. manubrium ; rad. c. radial canal ; 

 t. tentacle ; v. velum. (Prom Parker's Biology, after Airman.) 



