38 



THE HYDROMEDUSAE 



on the course of the coenosarcal canals, and often lies in a special 

 })it of the coonenchyme, termed the ampulla. An entocodon is not 

 formed in the usual way ; instead of this, which is an ectodermal 

 downgrowth to be hollowed out eventually into the subumbral 

 cavitv, the bodv wall at the sides of the generative cells grows 

 upwards, and arches over the manubrium to form the same cavity 

 (Millepora). All traces of raedusoid structure are lost in some 

 cases (male Distichopora). Kudial canals may be entirely absent 



II 





I 



:0-- 



•CD 7 5-eif!^r%i 



O' 



Fio. 4». 



Fk.. 4S<-. 



4Sb.— Piifninis iUiistratiin: the succt'ssive suigv's in the development of the cyclosystems 

 of the Styhvsteridae. 1, S/mouJuivim .■ i, S, AUoponx ; 4, 5, i^lylaster ; 6, A^^lus SHbriruiif ,- ', 

 .'^'■•' ■ • ■> ■■•1.., s, style : iij', daetylopore ;;;}>, gastroi<ore ; fc, in fig. (>, iuuer horseshoe- 

 > -•.ropore. (After Moseley, fK>m Laukester.) 



the corallum of Astit'.u-i fMbririiiis (one of the Stylasteridae), showiug 



c>v. .. -. ...- , ; at inten-als on the branches, each with a cenu^al gaslxv)i>ore and zone of 



siit-iike uactylopores. (After Moseley, from Laukester.) 



(Millepora), or may be present in varying numbers (twelve in 

 female Distichopora). 



Reproduction. — Asexual gemmation of hydroids is apparently 

 of the usual laminar character. The development of the sexually- 

 produced embryo has not been traced. 



Order 6. Siphonophora. 



Definition. — Colonial free -swimming Hydromedusae with 

 numerous polymorphic modifications of both hydroid and 



