SPECIAL MORPHOLOGY AND TAXONOMY OF SARCODINA 335 



initial shell is measurably larger than the initial chamber of the 

 organism which formed the amoebulse and is called a macrospheric 

 chamber as opposed to the microspheric chamber of the first genera- 

 tion, A new multi-chambered shell is then formed according to 

 the type of structure of the species. When fully grown the proto- 

 plasm of this macrospheric generation breaks up into a swarm of 

 small biflagellate flagellispores which leave the parent shell and 

 swim about by means of their flagella. These flagellates are 

 gametes which ultimately unite two by two to form zygotes. The 

 flagella are absorbed and the young zygotes secrete the shell material 

 of the first chamber about which other chambers are formed with 

 growth and budding division until the mature individual again 

 results. Thus there is a tj^pical alternation of generations in the 

 life history of a foraminiferon ; the microspheric individual starting 

 from a zygote, with its production of amoebulse is an asexual gener- 

 tion while 'the macrospheric individual starting from an asexual 

 spore, is the sexual generation giving rise to gametes. In Poly- 

 stomella the relative abundance of macrospheric and microspheric 

 shells is 38 to 40 of the former to 1 of the latter (Rhumbler, 1923). 



In classification, the form of the shell is usually given the first 

 importance while the substance of which the shell is composed is 

 secondary. There are so many t;^^es and variations of tj^^e in the 

 group that generalizations, useful for taxonomic purposes, are diffi- 

 cult. Certain plans of structure representing modes from which 

 variations appear, are evident however. Rhumbler recognizes five 

 of these main types as follows : 



1 . The nodosaroid t;^"pe : With chambers arranged one behind the 

 other in a straight or slight curved line (Fig. 150). 



2. The spiral type: With chambers arranged in such a way that 

 an imaginary line passed through the mouth openings of the suc- 

 cessive chambers would be a spiral line. 



3. The cyclical type: With later formed chambers arranged as 

 circles about the initial chambers, the circular chambers being fur- 

 ther subdivided into small secondary chambers. 



4. The azerval type: The earlier chambers are arranged in a 

 spiral but the later chambers are heaped in an irregular mass. 



5. The textularid type: The chambers are arranged in one or 

 two linear rows. For classification see Key p. 353. 



Sub-class IV. AM(EB^A. 



When rhizopods are mentioned the mental picture in most cases 

 is Amoeba or some of its close relations amongst the Amcebsea. It 

 is not the largest group of rhizopods but some of the forms included 

 here are amongst the most common types of Protozoa, while their 

 apparent simplicity and enigmatic movement have given them the 



