68] 



The Classification of Lower Organisms 



described Proterospongia Haeckeli as a colonial organism of amoeboid and choano- 

 flagellate cells in a common matrix; he regarded it as a transitional form, important 

 as evidence of the evolution of sponges from choanoflagellates. According to Duboscq 

 and Tuzet ( 1937) it is no organism, but a stage in the development of an individual 

 sponge from one which has been damaged. In spite of this, the hypothesis that the 

 choanoflagellates represent the evolutionary origin of the sponges, and accordingly 

 of the entire animal kingdom, continues to appear tenable. 



Fig. 11. — Choanoflagellata : a, b, Monosiga spp.; c^ Phalanasterium digitatum; 

 A, Salpingoeca ampullacea; e, Salpingoeca Clarkii; i, Foteriodendron petiolatum. 

 c X 500, the remainder x 1,000. c-f after Stein (1878). 



