REPRODUCTION 215 



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 Difflugiinae 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 

 molded, 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. 11, p. 33). 



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. 19, 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 Chlamydomyxa, Nuclearia, etc., but even such 

 questionable indications are absent in many cases of recent inves- 

 tigation (Belaf, Stern, et al.), where reorganization, if it occurs at 

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

 elements. 



C. Division 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. With but few excep- 

 tions the division plane is through the center of the body and in a 

 plane at right angles to the long axis of the cell. The externals of 

 division are similar to division in other groups, with preliminary 

 division of the plastids and nuclei and final division of the cell body. 

 As in flagellates and some rhizopods the cup- or test-dwelling forms 

 divide within the parent cup, one of the daughter individuals migrat- 

 ing and forming a cup for itself. In some forms the daughter indi- 

 viduals may remain and share the old house (Cothurnia ingenita). 



Where a tightly-fitting cell-covering is present as in Coleps hirtus, 

 it is divided transversely and the missing parts are regenerated by 

 the daughter organisms (Fig. 73, A, B, C, p. 136). In some Infusoria 

 as in the other groups, division in many cases is incomplete, the 

 daughter individuals remaining attached end to end as in Polyspira 

 delagei or Haptophrya gigantea. Or daughter individuals may 

 remain attached by incomplete division of their stalks, thus giving 

 rise to arboroid colonies of different types (Vorticellidae mainly). 



In some forms, probably in the majority of ciliates, there appears 



