REPRODUCTION 217 



Complications in the division process accompany the presence of 

 shells and tests. Where these are chitinous or pseudochitinous, 

 they may also divide with the cell body {Pseudodifflugia, CocJdio- 

 podiuin). In other cases the individual divides within the shell, 

 after which one of the daughter individuals moves out and forms a 

 new shell, while the other one remains in the original test (Micro- 

 gromia socialis, Clathrulina elegaiis, etc., Fig. 102). In most cases, 

 however, a novel method of shell duplication found in no other divi- 

 sion of the Protozoa, has been developed. This process, known as 

 budding division, occurs throughout the group of the testate rhizo- 

 pods and is well illustrated by the classical example of Euglypha 

 aheohda first described by SchewiakofP (1888). Here after full 

 growth following vegetative activity of the individual, the pseudo- 

 podia are drawn in; water is then absorbed whereby the protoplasmic 

 density is greatly reduced and the volume increased. This is fol- 

 lowed by a process resembling pseudopodia formation, the proto- 

 plasm emerging from the parent shell opening as a ball or dome which 

 assumes the general form of the parent organism. A new membrane 

 of pseudochitin is formed about the extruded mass and on it the 

 silicious shell plates, preformed in the parent protoplasm, are now 

 cemented. In some forms, e. g., Arcella species, the chitinoid mem- 

 brane becomes the permanent shell of the organism, older shells 

 becoming brown or reddish by coloring due to oxides of iron; in other 

 forms as in the Difflugiinse the chitinoid membrane is covered by 

 foreign objects picked up and stored by the parent organism. In 

 all cases of budding division after the budded individual is fully 

 moulded, the nucleus divides and one-half passes into the protoplasm 

 of the new shell. The connecting zone of protoplasm between the 

 old and the new shell breaks out into pseudopodia and the two indi- 

 viduals separate (Fig. 10, p. 32). 



The various types of foraminiferal shells, nodosarine, frondicular- 

 ine and rotaline— may be interpreted as due to a similar budding 

 division, but without actual separation of the parent and bud proto- 

 plasm, the type being dependent upon the density of the protoplasm 

 at the time of protrusion from the shell mouth (Fig. 17, p. 38). 



There is very little evidence of reorganization of the protoplasm 

 at division in these rhizopods. The frequent withdrawal of pseudo- 

 podia and rounding of the body may be an indication of changes 

 going on within, as in CIdamydomyxa, Nuclearia, etc., but even such 

 questionable indications are absent in many cases of recent inves- 

 tigation (Belar, Stern, et ah), where reorganization, if it occurs at 

 all, must be in the make-up of the protoplasmic and undifferentiated 

 elements (see, however, infra, p. 484). 



C. Division and Reorganization in Infusoria.— Here in the most 

 highly differentiated forms of the Protozoa the processes of equal 

 division are complex and the protoplasmic changes far-reaching. 



