oj the Desmidieae and Diatomeae. 17 



before the penetration of the pollen-tube into the ovule, and its 

 rehition to tlu^ germinal vesiele, had been made out; — observa- 

 tions whieh that theory really no longer required for the esta- 

 blishment of its main question. And if among so many con- 

 firmatory experiments, a few negative results present themselves 

 — in what branch of human knowledge do we not meet with 

 similar pha^nomena ? The general rules of evidence hold good 

 in such cases. 



The same analogies, then, which lead us to recognize a fecun- 

 dation in the penetration of the spermatic body of (Edu(junium 

 into the mother-cell of the spore, in the mixture of that body 

 with the contracted contents of the mother-cell of the spore 

 (with Pringsheim^s ' fecundation-globule'), must necessarily lead 

 us to regard conjugation as a fecundation. It is distinguished 

 from the process in (Edognniam only by tiie fact that the por- 

 tions of cell-contents which become blended into one cell are of 

 equal size, and that there is not one of them provided with 

 apparatus by means of which, like the spermatic body of Qldo- 

 gonium by its cilia, it is moved onward until it reaches the cell 

 to be fecundated ; — both points, evidently, of no essential im- 

 portance. 



EXPLANATION OF PLATE L 



Fig. 1. Cosmarium tetraophfhahnum, at the commencement of conjuga- 

 tion. Mapjnified 300 diameters, like the succeeding figures. 



Fig. 2. Two inthviduals of the same Cosmarium in conjugation. 



Fig. 3. S])ore of the same Cosmarium, after the spiny outer coat has been 

 stripped off. The contents of the spore divided into two primor- 

 dial cells. 



Fig. 4. A spore treated in the same way in the succeeding spring, dehis- 

 cent. Two of the ilaughter-individuals have escaped from the 

 crack. 



Fig. 5. Cells of Hyalotheca dissiliens, just conjugated. The borders of 

 the old cell-coat may be detected on the gaping halves of the 

 right-hand cell. 



Figs. 6, 7, 8. Conjugated cells of the same plant, after the formation of 

 spores. 



Fig. 9. jNIinute Closterium (perhaps identical with R/iiiphidium), which, 

 like the Pulmoglaa rcjirescnted in figs. 1 1-22, occurred in thou- 

 sands on the surface of water in vessels used for the cultivation 

 of large water-plants. The cells entering into conjugation show- 

 very clearly the extrication of the conjugation-cell from the 

 old shell. Magn. 500 diameters. 



Fig. 10. Closterium acutum in conjugation : fi'om a preparation in dilute 

 glycerine. Magn. 500 diameters. 



Figs. 11-17. Palmoglnea, sp. in different stages of division ; fig. 16, treated 

 with tinctine of iodine; fig. 17, after keeping m glycenne. 

 Magn. 400 diameters. 



Figs. 18-22. The same Palmoglcpa, in different stages of conjugation; 

 fig. 22. conjugation of three individuals (from objects kept in 

 glycerine). 

 Ann. ^- Mag. N. Hist. Ser. 3. Vol. i. 2 



