100 



EMBRYOLOGY 



ance by the Interpolation of new small septa in regular order 



between the existing ones. 



Non-ßexiial reproduction in the form of fission and budding 



is found widely distributed in the Zoantharia ; by this means 



extensive colonies ai^e developed 

 in the skeleton-forming Corals 

 (Sclerodermata), whereas in 

 the group of non-skeletal Ac- 

 tiniaria (Malacodermata) the 

 individuals produced by fission 

 or budding usually separate 

 entirely, so that, with few ex- 

 ceptions (Zoantheaj), the forms 

 in this case remain solitary. 



Fig. 46.— Basal plate of a larva of 

 Astroides caJycularis, soon after at- 

 tachment, with twelve radial ridges 

 fafter Lacaze-Düthiebs, from Bal- 

 four's Comparative Entbryology). 



Budding in the Actiniaria has been 

 observed more rarely — Epiactis 

 (Veerill, ?), Gonactinia (Blochmann 

 TJND HiLGEu), Zoanthus. More fre- 

 quently reproduction takes place by 

 fission. This may divide the parent 

 animal into two nearly equal i^arts: either as longitudinal fission, which 

 begins at the oral disc and progresses toward the base, or takes the oppo- 

 site direction, or as transverse division, a kind of rei^roduction which has 

 been described in detail for Zonactinia prolifera by M. S.vks and by 



Fig. 47. — Two stages of transverse fission of Gonactinia prulifera. Sabs (after 

 Blochmanit und Hilgkk). 



Blochjunx und Hilger (No. 74), and which in its outcome presents strik- 

 ing resemblances to the divisions in Flahellum and Fungia described by 

 Semper, and to the process of strobilization in the Scyphozoa. In Go- 

 nactinia it is always young animals that undergo transverse division. 



