REPRODUCTION 243 



duction," he says, "may rightly be interpreted as a process of reju- 

 venation. Our continued amputations in these experiments provide 

 a substitute for the rejuvenating effect of reproduction" (1924, 

 p. 458). His further conchision that his results "indicate experi- 

 mentally, a potential immortality of the protozoan individual" 

 (p. 456) can scarcely be allowed on the basis of forty-two days' 

 experience. A single individual of Uroleptus mobilis has lived for 

 more than ninety days without dividing, and similar but younger 

 individuals have been cut as in Hartmann's experiments, to find out 

 if ciliates would sustain Child's conclusion. The results (not pub- 

 lished) were invariably negative, although Uroleptus is an excellent 

 type for this kind of work and invariably undergoes rejuvenescence 

 after conjugation and after endomixis (see Chapter XII). 



With unequal division by budding and multiple division there is 

 further evidence of reorganization with reproduction. The small 

 cells that are budded oft' contain none of the differentiated cellular 

 elements of the parent organism. The spores are likewise provided 

 with protoplasm whose activities are unhampered by accumulated 

 products. This is clearly evident in the asexual reproduction of 

 Plasmodium tivax (p. 242), and is well illustrated in forms where 

 specialized structural elements are indications of the differentiations 

 which the old protoplasm has undergone. Thus in Mycetozoa 

 some of the hundreds of nuclei degenerate and give rise to spiral 

 elaters which with their s])iral walls are made up of microsomes and 

 kinetic elements (Strasburger, Kranzlin), while parts of the proto- 

 plasm become differentiated into encrusting peridia and supporting 

 capillitia. All of these differentiations are left behind when the 

 spores are formed and distributed. Analogous somatic structures 

 are also characteristic of the spore-forming stages of some types of 

 Gregarinida and Myxosporidia. In the former the spore-contain- 

 ing organs are either relatively simple spore cysts as in Monocystis 

 types (Fig. 179, p. 420) or more complicated structures— sporangia 

 —of some polycystid gregarines {e. g., Echinomera hispida or Gre- 

 garina cuneata). In the former the spores are dispersed b}^ the 

 formation of gas which bursts the cyst membranes. In the latter, 

 finger-formed tubes are developed from the peripheral protoplasm 

 of the cyst. These are formed from residual "chromidia" which 

 collect in rings al>out the peripher^' and from which the finger- 

 formed tubes grow into the mass of developing zygotes (Fig. 121). 



When the cysts are mature absorption of water causes the rupture 

 of the cyst walls, the tubes are forced out and evaginated as an 

 inturned glove finger may be blown out. The spores then are 

 distributed through these hollow tubes or sporoducts. 



In Myxosporidia still more complicated structures recalling the 

 capillitia of Mycetozoa, are characteristic of the spore-forming 

 stages. In Sphcpwmy.ra sahrazesi according to Schroder (1907) and 

 in Myxoholus pfeifferi according to Keysselitz (1908) the internal 



