XII.] CONJUGATION AND SEXUAL REPRODUCTION. \-j-J 



conjugation and fertilization is firmly established, more espe- 

 cially since the investigations on the conjugation of Infusoria, 

 begun by Butschli, have been carried to a high degree of com- 

 pleteness by the work of Balbiani, Engelmann, Gruber, R. 

 Hertwig, and above all by the exhaustive and wonderful in- 

 vestigations of Maupas^ 



But even if we may at length regard the agreement between 

 the processes of reproduction and conjugation as firmly estab- 

 hshed, and the ideas of an earlier date confirmed, we cannot, in 

 my opinion, retain the former conceptions as to the deeper 

 significance of these two processes. Both conjugation and 

 fertilization appear in an entirely new light if, — leaving behind 

 all ancient prejudices, and without bias — we examine and 

 compare them from the standpoint of our present knowledge. 

 Each process throws hght upon the other, and the true meaning 

 of both is thus made clear. 



I will first briefly recapitulate the facts of conjugation as 

 established by Maupas and ably confirmed and extended by 

 R. Hertwig, and I have therefore appended in Fig. XL a free 

 rendering of Maupas' figures, which illustrate the changes in 

 the nucleus accompanying the conjugation of Paraniaecium 

 caudaiimi. M indicates the macronucleus, ni the micronucleus ; 

 in} and m^, in figure 3, signify the two daughter-nuclei which 

 arise from the first division of the micronucleus ; m^ — ;;/*, in 

 figure 4, the four grand- daughter-nuclei of the same, derived 

 from the fission of the daughter-nuclei. In figure 5, three of 

 these, m^— m'^, are already disintegrating, while the fourth, ///', 

 is drawn out into a spindle preparatory to division, and the 

 consequent formation of the two reproductive nuclei, Cop^ and 

 Cop'\ Figure 6 shows the reciprocal transference of the male 

 reproductive nucleus from each animal into the other ; and 



^ We should read the admirable work of Maupas with even greater satis- 

 faction if it contained fewer reflexions upon those who have worked in 

 the same field. Maupas should not have forgotten that even the ablest 

 cannot avoid error, and that it is the fate of all work, even the most 

 excellent, to be in time surpassed ; — for upon this the whole advance of 

 science depends. We may correct the mistakes of our predecessors 

 without forgetting that we stand on their shoulders. The very power 

 we possess of improving on them is largely due to the fact that they have 

 placed their successors upon a higher level than that from which they 

 started themselves, and it is but a poor return for this to label their woi k 

 'superficial,' ' inaccurate/ &c., &c. 



VOL. II. N 



