112 BIOLOGY OF THE PROTOZOA 



down the left side of the peristome closely following the bases of the 

 frontal and peristomial membranelles. In the anterior lip it gives 

 rise to a simple network of branching fibrils (Yocom). The other 

 cirri of the ventral surface are not thus connected with the motorium, 

 and each appears to ha^•e an entirely independent set of fibers which 

 run into the endo])!asm and disappear in difi^'erent directions. 



Yocom attempted, rather unsuccessfully, to homologize the 

 motorium with the blepharoplast of flagellates; until further obser- 

 vations are forthcoming in regard to the activities of this structure 

 at different periods of cell life, it seems more expedient to regard the 

 motorium as a structure peculiar to the ciliates than to add it to 

 the already over-burdened conception of the blepharoplast. 



The only direct evidence of the physiological nature of the neuro- 

 motor complex is furnished b^^ Taylor's micro-dissection experi- 

 ments with the same organism, Eiiplotcs patella. Cutting the fibers 

 connecting the anal cirri with the motorium had a noticeable effect 

 on the normal reactions of creeping, swimming and turning, while 

 severing the membranelle fiber led to characteristic irregularities 

 in the usually coordinated activities of the membranelles and to 

 abnormal spiral revolutions while swimming. Destruction of the 

 motorium finally resulted in uncoordinated movements of the mem- 

 branelles and of the anal cirri. This evidence, excellent as it is, 

 rests upon an exceedingly delicate technic and upon the personal 

 inter])retation or estimation of minute differences between normal 

 and induced reactions. It is a line of work, however, which invites 

 further research and promises fruitful results. 



4. NUCLEAR DIVISION AND THE PROBLEM OF CHROMO- 

 SOMES. 



The aggregate of substances which have been described in the 

 preceding pages make up living protoplasm. Each type of sub- 

 stance receives from the food sui)ply, either directly or indirectly, 

 materials for the up-building of its own type, the sum total of such 

 processes constituting growth. Each type of substance, and each 

 granule, grows to its limit of size and then divides, reproducing its 

 like, a phenomenon which finds its visible expression in the division 

 of pyrenoids, mitochrondria, basal bodies, blepharoplasts, parabasal 

 bodies, nuclei, and finally the cell itself. Reproduction of the cell 

 of a protozoon thus involves reproduction of all its parts. 



The nucleus is tiie most complex of the formed organoids of the 

 cell and its reproduction involves growth and division of its different 

 elements. These may be more or less independent in their division, 

 or they may be M'ilcd in various simple or complex combinations 

 during the divi-Siii j>rocesses. Or the nuclear elements may be 

 combined with extra nuclear, cytoplasmic elements to form a char- 



