ox DEVKLOP-AIENT ETC. OF PHOROXIS. 'J/O 



cavity ])eeomes after luotainorpliosis tlic tentacular vessel of the 

 adult, as will soon 1)e further explained. 



Concurrently with the growth of the aduk collai' cavity the 

 larval cavity reci})rocally diminishes iu extent, and linally after 

 metamorphosis it is reduced to a uarrow cavity sui'rounding the 

 gut in front of the postoral septum : this is the ring ceèsel of the 

 adult. In lig. Go, which is taken from a transverse section through 

 the tentacular region of a larva (type ^1) just undergoing uieta- 

 morphosis, a semicircular S])ace {cir.c.) on the left side of the gut 

 reju-esents the greath' reduced larval collar cavity or the ring 

 vessel, which is found dorsally attached to the somatic walls and 

 is laterally (juite independent of the latter, though ventrally it is 

 fused with, and rests on, the postoral septum (vies.). Due of the 

 tentacular ves;ïels which proceeds from the ring vessel {cir.c), is 

 denoted in the plate l)y t.j: Fig. 64 e also shows a transverse 

 sectiou of th<i head portion (or a frontal section through the 

 supraseptal portion) of another partly metamorphosed larva re- 

 presented in fig. 11. Here a comparatively spacious cavity (c'i>*.c.) 

 surrounding the gut and filled with the corpuscles, represents the 

 ring vessel tVom whi(di the tcntiuadar vessels are given ott', though 

 this is not shown in the figure. In the ahove two fio'ures the 

 adult cavity distinctly a})pears as a narrow space {s.c.c.) outside of 

 lh<' ring vessel (cir.c.). In these stages of the metamorphosis, 

 the Itoth dorsal ends of the adult collar cavity become continuon- 

 wiih c;ich other so as to form a completely circular space above the 

 post(jral se})tum. 



I am still uncertain as to how this indinient of the ring vessel 

 comes into couununication with the dorsal vessel or with other 

 vascular spaces which make their appearance during nietamorj)hosis, 

 for it is almost impossible to obtain larva' of intermediate stages 



