245 



AssHETON ^ ) has really proved that the embryo (i. e. the sexual 

 generation) is not formed by the segmentation of the egg, but by a 

 proliferation in a totally difierent direction, i. e. in a zone which 

 gradually grows backwards whilst proliferating in front. In other 

 words, his researches may be explained as showing how the gameto- 

 zooid arises from an aposporous tissue within a larval or asexual 

 generation resulting from the segmentation of the egg — from the 

 so-called "primitive streak". 



The pole-mesoderm cells of Hatschek may also be mentioned, 

 and it may be suggested that a possible interpretation of them would 

 be that they might represent spore-mother-cells, which had of course 

 undergone no reductio-j. 



The Conjugation of the Infosoria and the Meaning of the 



Processes involved. 



By J. Beard. 



It has been specially interesting to study the conjugation processes 

 of this group in the light of experiences formed elsewhere. As is 

 well known , the facts have not been gleaned without the arduous 

 labours of many distinguished investigators. The processes appear to 

 be difficult of observation , but , thanks to the brilliant work of R. 

 Hertwig -) and E. Maupas ^), our knowledge of them has advanced 

 enormously in recent years. 



It may appear presumptuous to offer an explanation of the mean- 

 ing of the very complicated process, but, if apology be called for, it 

 may rest on the ground that it appeared necessary to put the theo- 

 retical "law of reproduction" to the test in this case also. If it 

 sufficed as an explanation of the facts, so much the better; if it 

 were found wanting, so much the worse. 



The one fact that would be fairly decisive appears to be lacking, 

 or at any rate, incompletely known. This is as to the precise point 

 at which the chromatiu-reduction takes place. 



Theoretically, as will be presently proved, such a reduction at 



1) R. AssHEToN, The Growth in Length of the Frog Embryo. Quart. 

 Journ. of Micros. Sc, Vol. XXXVII, N. S., p. 223—243. 



2) R. Hertwig, Ueber die Conjugation der Infusorien. Abhandl. d. 

 bayer. Akad. d, Wiss. II. CL, Bd. 17, 1889. 



3) E. Maupas, Le rajeunissement karyogamique chez les cilia's. Arch, 

 de zool. exper., 2. Serie T. VII, 1889. 



