942 



SCIENCE. 



[N. S. Vol. XII. No. 312. 



during fertilization, has exactly the same 

 significance. In Actinosphodrium eichorni the 

 encystment is connected with multiplica- 

 tion, but the multiplication (making of the 

 primary and secondary cysts) precedes fer- 

 tilization, and the fertilization itself (fusion 

 of the secondary cysts) leads to a resting 

 period of considerable duration (making 

 of the germ spheres). 



In the Protozoa then a lessened power of 

 division follows upon fertilization. In many 

 Gregarines encystment is certainly accom- 

 panied by fertilization, for the division into 

 pseudo-navicellse, which in turn separate into 

 the sickle-shaped germs, begins within the 

 cyst. In the Gregarines proper, multipli- 

 cation seems to be restricted entirely to this 

 encj'sted condition. In some Sporozoa, on 

 the other hand, there are two kinds of divi- 

 sion. Coccidiae and Hsemosporidise multi- 

 ply in the tissues of their hosts by division 

 and without fertilization (auto-infection). 

 At length, however, peculiar divisions begin 

 which are characterized by two things, (1) 

 that they are prepared for by fertilization 

 and (2) that the transportation from one 

 host to another is necessary for their proper 

 course. The fertilization may be completed 

 in the old host, but the multiplication is 

 connected with the transportation into a 

 new one or with some change of place. 

 Since a regular cycle between division with 

 and division without fertilization is here 

 established and each kind of division has 

 its peculiarities, we may speak of an alter- 

 nation of generations as Schaudinn has 

 done. Another illustration of alternation 

 of generations would be the reproduction 

 of Noctiluca. This form multiplies for a 

 long time by ordinary fission. Cross- fer- 

 tilization then takes place between two in- 

 dividuals, each of which produces a gen- 

 eration of zoospores, which in turn grow up 

 to NoctilucoB. According to Schaudinn's de- 

 scription, Trichosphcerium sieboldi is still an- 

 other example. 



The above resume shows that in all the 

 cases cited multiplication by division, and 

 after a time the advent of fertilization, is 

 constant. There is, however, the greatest 

 diversity in the relation between fertiliza- 

 tion and division. There are three possible 

 cases, (1) the fertilization is the^cause which 

 stops the division ( Volvox, Actinosphmrium, 

 Actinophrys) , (2) the fertilization is the 

 cause which brings about division of another 

 sort which is often very rapid (Noctiluca), 

 (3) the fertilization has no marked influ- 

 ence upon the power of division, because 

 the same kind of division prevails after fer- 

 tilization as before. 



In view of these facts is it possible to 

 speak of ' sexual ' reproduction in the Pro- 

 tozoa ? I think we cannot use such a desig- 

 nation without causing false conceptions of 

 the relation between reproduction and fer- 

 tilization. There exists in the Protozoa 

 only one kind of reproduction, t. e., division 

 in its manifold varieties. Besides this the 

 Protozoa need to reorganize the structure 

 of their unicellular bodies by fertilization. 

 What the nature of this reorganization is, or 

 its physiological significance, I will not at- 

 tempt to discuss. 



Fertilization is thus interposed from time 

 to time in the life history of a Protozoan. 

 The life epoch at which this interposition 

 occurs is often connected with the times of 

 more subordinate importance. It depends 

 upon suitable conditions which always vary 

 according to the conditions of life in the 

 different classes and orders and perhaps 

 even in the families of the same order. In 

 many Protozoa division takes place within 

 the cyst in a manner somewhat similar to 

 what occurs without the cyst in others. 

 Since we attribute no great significance to 

 these differences in encystment, so it would 

 be a mistake to emphasize the question 

 whether the division of a Protozoan was or 

 was not brought into close connection with 

 fertilization. In the Protozoa fertilization 



