140 THE PROTOZOA 



(p. 407) and allied organisms, where it is far from certain that the two nuclei 

 or cells, from which ultimately the pronuclei or gametes arise, have a common 

 parentage. Autogamy has recently become very fashionable, and there is 

 a tendency to regard as such, not only many cases which are probably truly 

 heterogamous, but also nuclear fusions or appositions which are not in any 

 way sexual (e.g., Schilling, 134). 



The essential point to consider, in cases of autogamy, is whether there is 

 a union of chromatin derived from distinct strains amphimixis or from 

 a common parentage automixis. Thus, it has been pointed out above that 

 in gregarines two gametocytes may associate, and even fuse into one body, 

 but with the nuclei remaining distinct (Fig. 71, B). When gamete-formation 

 takes place in a " neogamous " species of this type, the gametes of one sex 

 derive their pronuclei from one gametocyte-nucleus, those of the opposite 

 sex from the other, with subsequent syngamy of a truly heterogamous type. 

 If the fusion of the gametocytes were to go farther, a plastogamic, non-sexual 

 union of the two nuclei might result, producing a single nucleus containing 

 chromatin from two distinct sources ; in that case, when gamete-formation 

 took place, the syngamy would be, to all intents and purposes, a typical case 

 of autogamy, and would certainly be so described if it were not known that 

 the single gametocyte-nucleus had arisen by fusion of two distinct nuclei. 

 If, however, in each couple of copulating gametes, one pronucleus contained 

 chromatin derived from one of the two original gametocyte-nuclei, the other 

 pronucleus, similarly, chromatin derived from the other nucleus, the result 

 would be a true amphimixis, just as in ordinary heterogamy. 



In Actinosphcerium, plastogamic fusions of the ordinary vegetative, multi- 

 nucleate individuals are stated to be of common occurrence ; it is therefore 

 possible that an individual which encysts may contain frequently nuclei 

 from distinct sources. According to Brauer, fusion of nuclei takes place in the 

 mot her- cyst to form the nuclei of the primary cyst. There is therefore at 

 least a possibility that the autogamy of ActinospJicerium may be, in some 

 cases, combined with amphimixis. 



In other cases, however, such as Entamoeba coli and Amoeba albida (Fig. 87), 

 there seems little reason to doubt that the autogamy is a true automixis. 

 Analogous cases of self-fertilization are well known in flowering plants, where 

 they are sometimes the rule, sometimes an alternative to cross-fertilization. 

 In free-living Ciliata, also, syngamy has been observed between cousins, the 

 descendants of an ex-conjugant after but four divisions (Jennings, 121), 

 which is not far removed from automictic autogamy. 



The conclusion put forward above, on experimental grounds, 

 that syngamy has a strengthening or invigorating effect on the 

 cell-organism, receives further support from the many instances in 

 which it is observed to occur as a preliminary to the production 

 of resistant stages destined to endure unfavourable conditions of 

 life. Thus, in free-living Protozoa syngamy occurs commonly in 

 the autumn, previously to the assumption of a resting condition 

 in which the organisms pass through the winter. In Difflugia, 

 for instance, syngamy in the autumn is followed by encystment. 

 and the cysts remain dormant until the spring. This is strictly 

 comparable to the state of things known in many Metazoa, such as 

 Rotifers, Daphnids, etc., where in the summer soft-shelled eggs 

 are produced which develop parthenogenetically, but in the autumn 

 hard-shelled winter-eggs are produced which require fertilization. 

 In parasitic forms, such as Coccidia and Gregarines, syngamy is 

 related to the formation of resistant cysts which pass out of the host 



