624 H. S. Jennings 



of the parent cell as would cause at fission the production of such 

 an appendage on each of the progeny. 



At first thought it appears difficult to conceive how this could 

 occur. This will be made easier, perhaps, by a consideration 

 of the origin of certain characteristics in the race a (Fig. 4, etc.). 



Examples of Modifications from which Nezu Inherited Charac- 

 ters Might Result 



Let us take first the origin of the spine whose history is traced 

 in Fig. 4. The original ancestor of the race a was without spines. 

 But it was so deformed and modified that at the time of fission 

 two short teeth were produced during the processes of division 

 (Fig. 3, ^). At the next fission one of these short teeth formed as 

 it were a region of weakness, where a long spine was pushed out, 

 as an accompaniment of the processes of fission (Fig. 3, ^' ^). 

 Such a region of weakness might well exist without a visible tooth 

 to show its position; then at fission a spine would be produced in 

 this spot. It is evident that active physical and chemical processes 

 are in progress at the time of fission; these may easily result^ under 

 the influence of a local modification of the parent cell, in the push- 

 ing out of a spine or other structure of characteristic form. 



How such a new structure might appear in each of the progeny 

 of each generation is illustrated in a simple way by certain other 

 phenomena seen in the race a. As we have already set forth, the 

 progeny of a showed after a certain period a tendency to remain 

 united in chains. At the same time there appeared among the 

 free progeny o£ a 3. considerable number of individuals which bore 

 at one or both ends a spike-like point (Fig. 22). This character 

 did not become general, but so many cases appeared that one 

 might say that there was an inherited tendency toward this. Ob- 

 servation of the process of fission showed that these points arose 

 by the pulling out of the protoplasm while in the plastic condition 

 at the time of fission; the two young animals were connected, at a 

 certain stage, by a bridge of this plastic protoplasm. By their 

 movements they drew this out to a long strand, which finally broke 

 at the middle, leaving a point at the ends of the two animals. 



