96 



PHYSIOLOGICAL ACTIVITIES OF THE PROTOZOA 



chromidia form, gives rise to numerous buds, each of which is pro- 

 vided with chromidia, but with no part of the vegetative nucleus. 

 Such buds uhimately form the conjugating gametes in forms Kke 

 arcella, difHugia, centropyxis, etc. In parasitic forms hke Entavieba 

 histolytica, the cause of tropical dysentery, or Neurorydes hydrophobia , 

 the cause of rabies, there is a similar bud formation, the buds having 

 the characteristic chromidia; their further fate, however, is unknown, 

 the sexual processes of these organisms not having been made out 

 (see p. 303). 



A much more highly evolved method of division is found in some 

 of the colony forms of protozoa, where, as in Gonium ■pectorale (Fig. 

 35), for example, each of the sixteen cells of the parent colony 

 forms simultaneously a daughter colony of sixteen cells. Here 



Fig. 34 



Endogenous budding in Suctoria. (After Biitschli.) A, B, two stages in the formation 

 of the bud in Tokophrya quadripartita, CI. and Lach.; c, the bud liberated as a "swarmer;" 

 C, buds (e) in Acineta tuberosa, Elir. ; d, a bud liberated. 



simple division is followed by association of the daughter cells, and 

 individuals result which have passed through an actual, although 

 primitive, ontogeny. 



In spore formation, finally, we find one of the most prolific methods 

 of reproduction known. Here the organism breaks down simultane- 

 ously into great numbers of daughter elements, each dissimilar to the 

 parent in size if not in other characters. This process, involving as it 

 does the cessation of normal vegetative life with its ordinary processes 

 of digestion, assimilation, etc., usually takes place under the protection 

 of an outer covering or cyst, such encystment being a common phe- 

 nomenon among the protozoa, an outer covering of gelatinous material 

 l^eing thrown out on the surface of the organism whenever the condi- 

 tions of the environment become unsuitable. This investment becomes 



