158 CONJUGATION, MATURATION, AND FERTILIZATION 



begin to swell and to metamorphose into four new macronuclei, while 

 four remain as micronuclei. In the meantime, the two conjugating 

 cells separate soon after the interchange of micronuclei, and the pro- 

 cesses of reorganization are carried out independently. The old 

 macronucleus begins to disintegrate by first forming a skein-like 

 structure and then breaking down into granules which are finally 

 absorbed in the cell protoplasm. The process of reorganization 

 requires from one to three days before the first division of the fertilized 

 cell, which, as we have seen, contains four micronuclei and four 

 macronuclei. The daughter cells after the first division each contain 

 two macronuclei and two micronuclei, and the normal nuclear rela- 

 tions are not reestablished until after the second division, when the 

 resultant four cells have each one macronucleus and one micronucleus. 



This phenomenon may be interpreted in terms of the conjugation 

 in opalina, where minute ciliated cells conjugate, fuse, and form a 

 zygote (Neresheimer), if we assume that each of the daughter micro- 

 nuclei formed represents the nucleus of a microgamete in some phylo- 

 genetic ancestral stage, and if it is further assumed that in successive 

 phylogenetic stages (1) coupling of the adults occurred, as in grega- 

 rines; then (2) formation of endoplasmic gametes, as in ophryocystis; 

 and (3) interchange of micronuclei or gametic nuclei without the 

 formality of endoplasmic gamete formation. The vorticellidffi show 

 an aberrant development in such a hypothetical history, for here one 

 of the conjugating cells is smaller than the other and fuses with it. 

 But here as many as eight micronuclei (Maupas) may be formed in 

 the preparatory stages, a number difficult to explain on any other 

 hypothesis. Copulation, therefore, as seen in the infusoria, involving 

 temporary union of two similar cells, may be interpreted as a regression 

 of the gametes or a reminiscence of gamete formation in ancestral 

 cells, and as entirely different in its essential character from processes 

 of coition of the higher animals. 



2. Anisogamy. — Under this term the greatest number of hetero- 

 geneous phenomena are usually collected, and in all probability there 

 is a wide physiological difference between them, involving in some of 

 the higher types all of the characteristics of sex differentiation. In 

 those cases where size differences are not obligatory, as in polytoma, 

 for example, it is hardly justifiable to speak of sex differentiation, by 

 which is usually meant the formation of definite somatic characters in 

 individuals destined to form either eggs or spermatozoa. So far as the 

 ultimate products are concerned, the protozoa give evidences of a 

 gradual evolution towartl complete dimorphism of the conjugating 

 gametes. This is particularly well shown in the gregarinida, where a 

 series of forms shows the gradual development into gametes that 

 might well be interpreted as eggs and spermatozoa (Fig. 69). In 

 coccidia and in hemosporidia there are similar varieties of forms. 



