194 NATURE AND AFFINITIES OF THE SPONGES. 



apparent not only in the matured condition of such a form as Phalansterium 

 where the collar is rudimentarily developed but also in the ontogeny 

 or individual life-history of all other collar-bearing zooids, and which, 

 whether they belong to the simple and independent Choano-Flagellata or 

 to the interstitial system of a complex sponge-stock, commence existence 

 as similar collarless uniflagellate monads. 



