50 



ZOOLOGY 



SECT. 



the character, not of a single cell, but of a cell-colony, formed of numerous cells 

 connected by a non-protoplasmic substance. Chlamydomyxa, on the other hand, 

 has the character of a single cell, and no nuclei have been found in the spindles. 

 Thus further investigation is necessary before the association of these two 

 organisms in one group is fully justified, and it has recently been proposed to 

 include Labyrinthula among the M'ycetozoa. 



ORDER 3. FORAMINIFERA. 



General Structure. The members of this order differ from 

 the Lobosa and agree with the active phase of Chlamydomyxa in 

 the fact that their pseudopods are long and delicate, and unite to 

 form networks ; moreover, with few exceptions, they agree with 

 Arcella and its allies in possessing a shell. In the majority of 

 cases this shell is formed of calcium carbonate. 



One of the simplest members of the group is Microgromia (Fig. 

 32). It consists of a protoplasmic body (B), with a single nucleus 



FIG. 32. Microgromia socialis. A, entire colony; B, single zooid; C, zooid which 

 has undergone binary fission, with one of the daughter-cells creeping out of the shell ; 

 D, flagellula ; c. vac. contractile vacuole ; nu. nucleus ; sh. shell. (From Butschli's Protozoa. 

 after Hertwig and Lesser.) 



(mi.) and contractile vacuole (c. vac.), enclosed in a chitinoid cell- 

 wall or shell (sh.) with an aperture at one end through which the 

 protoplasm protrudes and is produced into delicate radiating 

 pseudopods. The animal multiplies by binary fission, and the 

 individuals or zooids thus produced remain united in larger or 

 smaller clusters or cell-colonies (A). Sometimes the cell-body of a 

 zooid divides, and one of the daughter-cells creeps out of the cell- 

 wall (C), and, after moving about for a time like an Amoeba, draws 

 its pseudopods, assumes an oval form, and sends out two 



in 



tiagella by means of which it is propelled through the water (D). 

 We shall find other instances in which the young of a Rhizopod is 



