DERIVED ORGANIZATION— TAXONOMIC STRUCTURES 165 



ent spiral roll of the collar being due to the presence of two pre- 

 hensile tentacles. In some cases two such collars, one within 

 the other, are present as in Salpingoeca entzii or S. marinus (Fig. 

 92). The second, outer, collar in some types is regarded by Doflein 

 as a periplastic rigid structure which forms a part of the cup or 



Fig. 92. — Types of choanoflagellates. A, Codosigapulcherrimus; B, Diplosigasocialis, 

 C, Salpingoeca marinus; D, collar type according to France. (After Calkins.) 



house and is not morphologically equivalent to the inner collar, 

 which, like a pseudopodium, may be shortened or lengthened, or 

 drawn in and formed anew by the living cell. According to the 

 older interpretation these protoplasmic collars assist in food-taking 

 by forming a sticky directive course for particles down the inside 



