82 



HARDWICKE'S SCIENCE-GOSSIP. 



sisted of numerous caps tilted one over the other 

 (Figs. 72 : 2, and 72 : 4). 



OEdogonium has a sexual and asexual method of 

 reproduction ; the latter is effected by zoogonidia. 

 The contents of any cell are converted into a zoo- 

 gonidium, which in due time escapes from its mother 

 cell (Fig. 72 : 5), and germinates (Fig. 72 : 6). 



Frequently the contents of a still unicellular oedo- 

 gonium produce a zoogonidium, which escapes and 

 germinates in the same way as the ordinary zoo- 

 gonidium. 



As regards the sexual method we have monoecious 

 and dioecious filaments. Let us examine one which 

 has the male organs on it ; on this we will notice here 

 and there two or more cells, abutting on each other, 

 but of much smaller longitudinal diameter than the 

 ordinary cells. In each of these two zoospores are 

 formed, which for some reason, which we will see 

 later on, are called not antherozoids, but androgonidia 

 (Fig. 72 : 4). We will now pass on to the examination 

 of the female organ, or oogonium. This consists of a 

 thick cell-wall with a small gap on one side, and is 

 of a more or less round shape, being flattened, where 

 it abuts at both ends on to the remaining part of the 

 thallus ; it contains the oosphere, or egg-cell. We 

 will now go on with the androgonidia. They are 

 motile, and move about till they settle either on a 

 cell below or above the oogonium, or on the oogonium 

 itself (Figs. 72 : 8, 9, 10). Immediately they have 

 attached themselves they begin to germinate into the 

 so-called dwarf males. These consist of from two to 

 three cells ; the uppermost cell is the antheridium, 

 and contains one antherozoid (Fig. 72 : 8, 9, 10). 

 Fertilisation takes place by the antheridium losing 

 part of its cell-wall by a rupture (Fig. 72 : g), and, by 

 being applied more or less closely to the orifice on 

 the side of the oogonium, the antherozoid has no 

 great difficulty, after leaving the antheridium, in 

 getting into the oogonium. It is assisted in this act 

 by the oosphere, which partly sucks it in by sending 

 out a protoplasmic protuberance (Fig. 72 : 11). 



When the oospore is ripe, it is surrounded by a 

 thick investing membrane, and the whole oogonium, 

 having gradually detached itself from the remaining 

 part of the thallus, sinks to the bottom of the water, 

 where it passes through a period of rest, before again 

 germinating. The oospore has by this time acquired 

 a very strong red colour (Fig. 72 : 12). 



As a mounting medium, acetate of potash'has proved 

 theibest for all green fresh-water algse (and marine too), 

 as it does not in any way affect the green colour, and 

 hardly the cell contents in general. One has to be 

 rather careful, when using it, as it evaporates very 

 quickly when under a coverslip. 



I found all stages in the development of the repro- 

 ductive organs of CEdogonium very nicely in May, 

 in a pool near Rhoscolyn, Anglesey. 



Otto V. Darbisiiire. 

 • Balliol College, Oxford. 



NOTES ON NEW BOOKS. 



PRACTICAL MICROSCOPY— hy Geo. E. 

 JL Davis (London: W. H. Allen and Co.). A 

 young man taking up microscopic work could hardly 

 find a better helper than this book. It contains over 

 three hundred illustrations, and deals with every part 

 of the subject, from the structure of the human eye to 

 the recipes. It is now some years since we had the 

 pleasure of recommending this book when it first 

 came out, and, as every prophet likes to see his 

 prophecy fulfilled, we are glad to find that new 

 editions have been called for. In this latest edition, 

 Mr. Davis has very properly completely revised his 

 book so as to bring it down to the necessities of 

 modern times. The chapters on the improvement of 

 the structure of the microscope, and the microscopic 

 apparatus in use all over the world, will prove of 

 great value to the student. 



Dlctiona^-y of Photography, by E. J. Wall 

 (London : Ilazell, Watson and Viney). Some 

 months ago we had occasion to call attention to the 

 useful and timely articles which were appearing in the 

 "Amateur Photographer" under the above heading. 

 The work under notice is really a collection of the 

 above articles in the form of one of the handiest text- 

 books that any photographic student or worker could 

 desire. It will prove useful also lo others than 

 photographers, as a reference book on numberless 

 subjects connected with physics. 



The Naturalist in Siluria, by Capt. Mayne Reid 

 (London : Swan Sonnenschein and Co.). Readers of 

 this author's books will hardly be surprised to find 

 that in the present volume he is coming out purely as 

 a Natural History writer. All his novels and stories 

 of adventures are crowded with natural history 

 references. Capt. Reid resided in Woolhope, the 

 centre of the district termed by Sir Roderick 

 Murchison, Siluria. It is a wonderful country, as 

 every geological student knows who has wandered 

 through its green valleys and over its low-lying well- 

 wooded hills. Capt. Reid's book deals chiefly with 

 the birds of the district, and that in so pleasant a 

 form as to remind us of the novelist. A few of the 

 mammals come in for notice, and there are a number 

 of etceteras which make up a highly readable 

 volume. 



An Assistant to the Board of Trade Examination, 

 by Capt. Forbes (London : Relfe Brothers). The 

 want of a little manual to put in the hands of 

 candidates for Board of Trade examinations has long 

 been felt, and in this little book Capt. Forbes has- 

 done his best to meet it. We cordially recommend 

 it to those whose interest it affects. 



The Crnise of the Marchesa, by F. H. H. Guille- 

 mard (London : John Murray). This is one of the 

 most delightful books of natural history travel which 

 have appeared since Professor Moseley's " Cruise 

 of the Challenger." The scenic and biological de- 



