STRUCTURE AND LIFE-HISTORY OF VOLVOX GLOBATOR. 237 



by the decay of the parent-cell, and sinks to the bottom of the water to 

 hibernate. The subsequent history of these bodies has been traced by 

 Cienkowski, and more recently by Henneguay, (" Journal de Micro- 

 graphie," Vol. LL, p. 485, Bull. Soc. Philomath, Paris, July, 1878.) 



Cohn believed that they must be dried up before germination was 

 possible. Henneguay has now observed that this is not so. In spring 

 the outer case of the spore (exospore) is ruptured, and the swollen con- 

 tents (endospore) project through the opening. The contents then 

 divide gradually into two, four, eight, sixteen, or more small cells, which 

 become bright green, each meanwhile acquiring two vibratile cilia while 

 still contained within the inner membrane of the spore. The cells, at 

 first in close apposition, separate further from one another by interposi- 

 tion of gelatinous hyaline matter, the outer membrane disappears, the 

 cilia become active, and the young Volvox, already containing some 

 elements larger than the others and destined, in due course, to produce 

 daughter-spheres, moves freely through the water. " The spores of 

 Volvox, therefore, germinate in water, and each of them produces a single 

 colony by a process of segmentation identical with that which gives rise 

 to a daughter-colony at the expense of a cell of the mother-colony." 



The sequence of asexual generations is repeated for many months, 

 and in the following autumn the alternation of generations is again com- 

 pleted by the intervention of the processes just described. 



There are other phenomena of more or less exceptional occurrence 

 and of lesser interest in the history of Volvox, to which I might allude 

 did space permit, but those which I have traced constitute the essential 

 elements in the structure and life-history of this singularly beautiful and 

 interesting plant. I trust that I have succeeded in presenting to my 

 fellow-students a somewhat more complete and life-like account of them 

 than is accessible in ordinary text-books, and in showing how amply this 

 organism will repay careful and systematic observation. 



OKIGIN OF THE EOCKS AND SCENEKY OP 

 NOKTH WALES. 



by j. j. harris teall, m.a., f.g.s., etc., late fellow of 

 st. john's college, Cambridge. 



(Continued from page 219.J 

 Having discussed the origin of the more important varieties of "Welsh 

 rocks, I will now give a brief sketch of their distribution over the surface 

 of the country, of their order of arrangement, and of the order of their 

 formation. The facts I am now going to communicate are taken almost 

 entirely from Vol. Ill of the Survey Memoirs, and from the Survey maps. 

 Although the work recorded in these publications will have to be 

 remodelled, and in many important particulars entirely recast, yet it will 

 always command the greatest respect of all geologists. 



