602 MAECUS M. HAETOG. 



In the second paper we come to the study of conjugation, 

 and the first full account of it yet given, illustrated by ex- 

 quisite figures as well as by numerous diagrams, some of which 

 we shall reproduce in a modified form. The materials were 

 obtained by the methods described above, the starvation of 

 mixed colonies of a species at a suitable stage always bringing 

 about conjugation. In these experiments it was found that 

 the method of starvation and mixing colonies of different 

 stocks failed if tried too soon after conjugation, and this was 

 the starting-point of the discovery of the puberty of the cycle 

 mentioned above. 



In some cases (e. g. Leucophrys patula) the first result 

 of starvation is to induce the production of dwarf forms by 

 repeated fission, and it is only these dwarf forms that con- 

 jugate ; if, however, a food-supply be introduced at a suffi- 

 ciently early stage, the gametes quit company, and resume the 

 ordinary process of growth and bipartition. The formation of 

 similar dwarf forms occurs only in certain members of the 

 stock of Vorticellines, and eventuates in the production of the 

 microgaraetes or " males,^^ which swim to and conjugate 

 with the undivided attached megagametes. 



By careful observation the time for each stage of the process 

 was determined ; and by killing and fixing couples at successive 

 intervals, preparations of every stage were easily obtained for 

 research. The fixative was a 1 per cent, solution of corrosive 

 sublimate, and the animals were stained on the slide with 

 picro- carmine or a solution of methyl green in 2 per cent, 

 acetic acid, and then cleared in situ with glycerine or balsam. 

 The best homogeneous immersion objectives are absolutely 

 needed for a complete study of these processes. 



I may recall the fact that the nuclear apparatus of Ciliata 

 is double, comprising the large "meganucleus" (macronucleus, 

 endoplast, nucleus of authors), and the '' raicronucleus '' (endo- 

 plastule, paranucleus, or nucleolus) , which latter is multiple 

 in some species. In bipartition the meganucleus divides by 

 mere constriction, while the micronucleus shows all the stages 

 of karyokinesis save the disappearance of its membrane. In 



