240 
PROCEEDINGS OF SOCIETIES. 
rangium, afterwards attain the size of the parent species. "We have, in an 
interesting account by Hofmeister, lately .published ( loc.cit .), a descrip¬ 
tion of the germination of the sporangium of Cosmarium tetraophthalmum 
(ICg.); 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 
(Breb .) 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 (Schranh ) is described and figured in Balfs, but 
in this case the young brood were miniature resemblances of the mature 
form of that species. The sporangia of the Desmidiacese, 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 
this genus, do not escape separately, but are emitted en masse , still in¬ 
closed in the inner membrane of the parent cell, within which, however, 
they exert a vigorous movement, and involved still in which they settle 
down, and arrange themselves in a flat cluster, resembling that from one 
cell of which they originated. But a more general increase by zoospores 
has been attributed to the Desmidiacese, but I cannot find it corroborated 
by direct observation that this actually takes place. Certain it is that a 
peculiar motion (or commotion) of the granular contents not uncommonly 
* “Rejuvenescence in Nature,” Ray Soc. Publication, 1853 
