30 



POPULAR ILLUSTRATIONS OF 



passes into the ovary of the other. Here, as in the plant, the germs 

 of future Paramaecia are formed in the shape of round bodies. These 

 become of an oblong shape, then covered with cilia, and in this 

 form are set free from the parent cells, and start on their own 

 account as young fry in the great struggle for existence to which 

 the nomad as well as the man is doomed. 



But there are two other modes of propagation among the Infusoria. 

 To illustrate these singular phases in the life history of these lowly 

 forms of animal existence, let us examine the economy of the Vorti- 

 cellinae, considered by some as typical forms of the Infusoria. Fig. 27 

 is from a drawing of a group of Vorticella nebulifera, attached by 

 their stalks to a bit of the root of duckweed. They are seen in all 

 the positions they assume under the microscope, except that in which 



Fig. 27. Vorttcella nebulifera (highlymagnifled) a a, unfolding - 6 &, retracting c, dividing 

 d. bell separated from stalk, and having a posterior circlet of freshly-developed cilia. 



they simultaneously contract and draw themselves down to the root 

 to which they are attached. Their structure is not such as would 

 be inferred by the appearance of the group. Let us, therefore, fol- 

 low the history of an individual, say that one marked d, which is 

 seen to be falling away without a stalk. The bell has just been 

 developed by division, or fissiperation as it is termed the process 

 described in Paramaecium. The division is completed at c, and c? 

 has just separated from the animalcule whose stalk it is represented 

 as bending. Note, first, that this cup or bell has a series of cilia 

 provided for it at the end opposite to the mouth. These are its 

 principal locomotive apparatus, and by their means it swims about 

 in the water. When, however, it finds a place suitable for its pur- 

 poses, it becomes attached thereto by this end, and the locomotive 



