THE SARCODINA 99 



conjugate, and later form either double or multiple individuals (plas- 

 modia). 



The conjugation of swarm-spores of Reticulariida and Radiolaria 

 has not been observed, although the diverse size of the anisospores 

 in the latter group favors this view. In the fresh-water form, Hya- 

 lopns, which differs but slightly from the marine forms in regard 

 to reproduction, the swarm-spores actually conjugate, although the 

 development of the copula was not observed (Schaudinn, '94). 



INTER-RELATIONSHIPS OF THE SARCODINA 



In drawing conclusions as to the most primitive group of the Pro- 

 tozoa, there is need of extreme caution. Biitschli long since showed 

 that the development of the Protozoa, from spores or germs of any 

 kind, gives but little indication of their genetic affinities, and that 

 such affinities must be deduced from the study of the group as a 

 whole. 



In questions concerning the most primitive Protozoa, the Infusoria 

 are immediately thrown out, for, of all groups of Protozoa, they are the 

 most highly specialized, and along lines which have carried them 

 to the highest point of morphological development of the single cell. 

 The Sporozoa also have become highly specialized through their 

 parasitic mode of life. Neither of these groups therefore can be 

 said to have been the most primitive forms of Protozoa. Among the 

 Sarcodina, the Heliozoa and Radiolaria show abundant evidence of 

 descent from rhizopod-like ancestors, while a similar relation can be 

 assumed of the Dinoflagellidia and Cystoflagellidia to the Flagellidia. 

 It remains, therefore, to ascertain if possible which of the two 

 groups, Flagellidia or Rhizopoda, shows the more primitive charac- 

 teristics. Students of the Protozoa have differed widely on this 

 question. Biitschli avoids the difficulty by the assumption that the 

 beginnings of both are represented by the forms intermediate between 

 the two, and sees in the members of the family Rhizomastigidae 

 (Mastigamceba and its allies), the common stem-forms of Flagellidia 

 and Rhizopoda. On the other hand, the Rhizopoda, with their animal 

 mode of nutrition, must have had other forms of life as their source 

 of food, and from which they were possibly derived by the process of 

 metasitism. On this account, Klebs ('92) makes the Flagellidia the 

 original group, since here are retained forms which live to-day as the 

 original forms probably did, with the power to manufacture their own 

 food (Phytoflagellida). It is extremely difficult to choose between the 

 two assumptions, although the balance apparently lies in favor of the 

 view which Klebs advocates. From the variety of forms they assume, 

 the Flagellidia appear to have a greater power of adaptation than the 



