MORE COMPLICATED LIFE CYCLES 



123 



cell, they certainly are not connected with the formation of the gametic 

 nuclei. On the other hand, there can be no doubt of the propagative 

 nature of such distributed granules in the great majority of protozoa, 

 and in such cases we may, with reason, speak of a definitive germ 



FIG. 52 



a 



-r^ 9 



- -*, v^/.^ . 



D // '. 



Life cycle of Polystomella crispa S. (Lang and Schaudinn). A young form derived from 

 the union of two flagellated gametes (A) develops into an organism with microspheric type 

 of shell. The nucleus increases by mitosis until many nuclei are present when they break 

 up into granules of chromatin (B). The protoplasm fragments into reproductive bodies, 

 equivalent to merozoites (C), each having several granules of the distributed chromatin 

 ("Chromidien"). Each reproductive body (D) develops into an adult with a macrospheric 

 type of shell, and with nuclei in the form of small chromatin granules (-E). When mature 

 these forms fragment into hundreds of flagellate gametes (F) which conjugate, and so com- 

 plete the cycle. (See, also, Fig. 41, p. 114.) 



plasm as contrasted with the somatic plasm. With such an assump- 

 tion we are brought in touch with a problem of high theoretical interest 

 in general cytology, and with the protozoa, as with the metazoa, we 

 have this question to consider: Are there two kinds of substances in 



