146 COXJUGATIOX, MATVRATIOX, AXD FERTILIZATIOX 



germinal nuclei. The sporoplasm of the pansporoblast divides into 

 two parts (J/), the sporoblasts each containing six of the fourteen 

 nuclei, while the reduction nuclei remain outside. The six nuclei in 

 each sporoblast are thus differentiated into somatic and germinal 

 nticlei, fotu- in each case going into somatic modifications of the spores 

 (shells, pole capsules, and threads), and two, presumably one of each 

 of the original two kinds, remaining as pronuclei (X, 0, P). After 

 the spores are mature and only traces of the somatic nuclei remain, 

 these germinal nuclei fuse, so that the spores, when taken into a new 

 host, are uninucleate [P, Q). If, as Schroder suspects, the multi- 

 nucleate ameboid adult is formed by fusion of two or more cells, then 

 such a process would be like that of the mycetozoa and exogamic 

 rather than autogamic (p. 150). Observations, however, are wanting 

 to confirm this supposition, the many obstacles in the way of observa- 

 tions to this end making confirmation extremely difficult, btit the 

 other matters relating to ntmiber of nuclei formed, their fate, etc., 

 are well corroborated (see actinom\-xid£e, and Mi/.vobohts pfeiferi. 

 Fig. (31, A, I). 



B. FERTILIZATION BY ENDOGAMY (PEDOGAMY, PROWAZEK). 



The transition from atitogamy into endogamy, whereby the sexual 

 union is between descendants of the same original cell, is marked 

 by numerous intermediate stages which are sometimes described as 

 autogamous. The difference is largely one of degree only, and among 

 these intermediate forms, at least, to include them under one or the 

 other heading is mainly a matter of expediency. The principle under- 

 lying the distinction is, however, of considerable theoretical importance, 

 and the dift'erence which exists between the partially divided cell in 

 Eiitameba coU {see above) and the tmion of separated parts within 

 the same parent cell (see myxobolus and other cases below) is a differ- 

 ence which becomes magnified in higher types into all of the differential 

 characteristics which distinguish exogamic processes. 



The transition from atitogamy to endogamy is well shown in myce- 

 tozoa and myxosporidia , wherp , as may be seen, the dift'erence is only 

 one of degree. There are numerous examples of the phenomenon, 

 from which we select a few showing dift'erent grades in complexity, and 

 it should be noted that the same arguments as to the possible exo- 

 gamic nature of the processes apply here among the mycetozoa and 

 myxosporidia as well as in the cases cited above. 



Keysselitz ('OS) has quite recently described the process of pan- 

 sporoblast formation in a myxospore {Mi/.i-obolun pfeiffcri) which 

 dift'ers in one important respect from the process in spheromyxa. 

 Here the pansporoblasts which Keysselitz names the "propatjatiorL 



