ZOOLOQICAL AND BOTANICAL ASSOCIATION. 101 



interesting account by Hofmeister, lately published (loc. cit.) f a descrip- 

 tion of the germination of the sporangium of Cosmarium tetraophthalmum 

 (Kg.) ; and of the evolution therefrom, by segmentation of its contents, 

 of a brood of eight or sixteen young Cosmaria, and which, according to 

 his statement and figures, more resembled Cosmarium Meneghinii 

 (Brtb.) than C. tetraophthalmum. His observations do not appear to have 

 been continued long enough to prove that these young Cosmaria ulti- 

 mately grew into the mature form of Cosmarium tetraophthalmum ; but 

 there can, I apprehend, be no doubt they did, or would have done, in 

 their native habitat. It might, perhaps, hence appear probable that 

 Cosmarium Meneghinii is not a true species, but only the young state of 

 C. tetraophthalmum. However, if it indicate, as I should suppose it does, 

 that when a Desmid repeats itself by transverse division, it has attained 

 the mature size and form of the species, then must Cosmarium Meneg- 

 hinii be considered a good species, for I have myself met it in a divided 

 state. If this be so, then I apprehend all that can be inferred is, that 

 the young state of Cosmarium tetraophthalmum, immediately upon develop- 

 ment from the sporangium, greatly resembles the mature form of C. 

 Meneghinii. A very similar observation by Mr. Jenner on the sporangium 

 of Closterium acerosum (Schrank) is described and figured in Ralfs, but 

 in this case the young brood were miniature resemblances of the mature 

 form of that species. The sporangia of the Desmidiaceaa, as well as the 

 similar productions in other Algae, appear to be endowed with the power 

 of remaining dormant for a length of time (which is, perhaps, some- 

 times of some considerable duration) before their vegetative activity is 

 aroused, and this probably occasionally under a state of dryness which 

 would be fatal to the parent species. The following-out of the develop- 

 ment of the sporangium appears very difficult ; seldom is the happy op- 

 portunity presented to the observer. I have myself repeatedly had the 

 sporangia of several species, sometimes abundantly ; and while I have 

 been able to trace, for my own satisfaction, their formation (in Arthro- 

 desmus incus) from the first approach of the parent fronds to conjugate, 

 to the ultimate perfecting of the fully formed sporangia, they, however, 

 in all cases, perished before any alteration in their appearance took place. 

 A mode of propagation by unquestionable zoospores has been noticed 

 and described by Alexander Braun, in Pediastrum.* The zoospores, in 



• " Rejuvenescence in Nature," Ray Soc Publication, 1853. 



