214 DEVELOPMENT OF MICROSCOPIC ALG^ AND FUNGI. 



this discovery, by Mr. Busk,* who noticed the fact of the 

 existence of rhythmical contractions in the single vacuole in 

 the zoospores of Volvox glohator. But the most remarkable 

 circumstance connected with this is the apparently precise 

 resemblance of the phenomenon in the two cases. Mr. Busk 

 states, that in Volvox tlie contractions occur very regularly at 

 intervals of 38'" to 41'" ; and Cohn's observations would show 

 that where two vacuoles exist in the same cell, the interval 

 for each vacuole varies between 25'" and 48'" ; and in a case 

 where but one existed, as in Volvox, the intervals, by observa- 

 tion, were 45, 43, 45, 42, 43, 40, 42, 41, 41'". The suddenness 

 of the contraction, and the gradual expansion of the vacuole, 

 are noticed by both observers ; in fact, the observations agree in 

 every particular, save only in the circumstance of the situation 

 of the contractile vacuole or vacuoles. Cohn says that he 

 always found them to be situated at the base, as it were, of 

 the cilia — whilst Mr. Busk states that, " it may be situated 

 in any part of the zoospore, or not unfrequently in the base, 

 or even in the midst of one or other of the bands of proto- 

 plasm, connecting it with its neighbours." 



This rhythmical contraction is, certainly, a remarkable 

 phenomenon in the vegetable kingdom, and worthy of attentive 

 consideration. It does not, as yet, appear to have been 

 observed, except in the above two instances, but will, doubt- 

 less, be found to exist in much more numerous cases. 



4. The observations on Hydrodictyon do not appear to 

 contain more than a very good summary of what is known on 

 that subject, and are illustrated by good figures. We shall 

 return at a future opportunity to this, perhaps, most interest- 

 ing of all vegetable productions. Upon which will also be 

 found very valuable information in A. Braun's work, above 

 referred to. At the conclusion of this part of his work. Dr. 

 Cohn propounds the following axiom : — That in the lowest 

 forms (fresh-water algae) a motile, primordial cell, is at the 

 same time the seat of germination (swarm-spore), whilst in 

 the higher cryptogamia, it is the fertilizing organ (swarm- 

 filament) ; on the other hand, in the latter a quiescent cell 

 (spore) is the seat of germination, whilst in the highest 

 phanerogams, an equivalent cell (pollen-cell) discharges the 

 function of a fertilizing organ. 



5, 'We observations contained in this part of the book 

 relate to the germination of Zygaema and Anabaiua. They 

 are of considerable interest, and will, with the preceding, 

 form the subject of a future notice or abstract. 



* Transactions of the Microscopical Society. ' Quarterly Journal of 

 Microscopical Science,' Vol. i., p. 31. 



