100 



EMBRYOLOGY 



ance by the interpolation of new small septa in regular order 



between the existing ones. 



Non-sexual reproduction in the form of fission and budding 



is found widely distributed in the Zoantharia ; by this means 



extensive colonies are developed 

 in the skeleton-forming Corals 

 (Scleroderraata), 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 (Zoan these), the forms 

 in this case remain solitary. 



Fig. 46.— Basal plate of a larva of 

 Astroides calycularis, soon after at- 

 tachment, with twelve radial ridges 

 (after Lacaze-Duthikrs, from Bal- 

 yocR's Comparative Emhryology). 



Budding in the Actiniaria has been 

 observed more rarely — Epiactis 

 (Verkill, ?), Gonactinia (Blochmann 

 UND Hilger), Zoanthus. More fre- 

 quently reproduction takes place by 

 fission. This may divide the parent 

 animal into two nearly equal parts : 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 reproduction which has 

 been described in detail for Zonactinia prolifera by M. Sars and by 



Fig. 47.— Two stages of transverse fissicn of GonacLinia prolifera. Sabs (after 

 Blochmanic uwd Hilgkk). 



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

 ing resemblances to the divisions in Flabellum and Fungi a described by 

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

 nactinia it is always young animals that undergo transverse division. 



