438 Bibliographical Notice. 



translatory movement, which soon causes their dispersion in the 

 circumambient fluid. These are the spermatozoids of P. hursaria. 

 Iodine, alcohol, and acetic acid instantly stop their movements ; 

 they are insoluble in the last-mentioned reagent when concen- 

 trated, although this dissolves all the other elements of the body, 

 with the exception of the green granules. 



It is usually from the fifth to the sixth day following the 

 copulation, that the first germs are seen to make their appear- 

 ance in the form of small rounded bodies, formed of a membrane 

 which is rendered very evident by acetic acid, and greyish, pale, 

 homogeneous, or almost imperceptibly granular contents, in 

 which neither nucleus nor contractile vesicle is yet to be distin- 

 guished. These organs do not appear until afterwards. The 

 observations of Stein and F. Cohn have shown how these embryos 

 quit the body of the mother in the form oi Acinetcs furnished with 

 knobbed tentacles, — true suckers by means of which they remain 

 for some time still adherent to the mother, deriving their nou- 

 rishment from her substance ; but their investigations did not 

 reveal to them the ultimate fate of these young animalcules. I 

 have been able to follow them for a considerable time after they 

 detached themselves from the body of the mother, and have con- 

 vinced myself that, after losing their suckers, becoming sur- 

 rounded with vibratile cilia, and obtaining a mouth which first 

 shows itself in the form of a longitudinal farrow, they definitely 

 acquired the form of the mother, becoming penetrated in the 

 same w'ay by the green granulations characteristic of this Para- 

 mecium, without undergoing any more important metamorphoses. 



BIBLIOGRAPHICAL NOTICE. 



A Cyclopaedia of the Natural Sciences. By William Baird, M.D., 

 F.L.S. London and Glasgow. Griffin, 8vo, 1858. 



That the prepnratiou of even a popular dictionary of the Natural 

 Sciences, including the wide range of Zoology, Botany and Mineralogy, 

 is a task from which any one man might be well excused for recoiling, 

 will be readily admitted on all hands ; — such a work is a gigantic 

 undertaking, in which complete success can hardly be looked for. 

 In the present case, the difficulty is not lessened by the fact that the 

 information to be communicated on tliis extensive series of subjects 

 had to be selected and compressed, so as to occupy only a single 

 volume ; and although this is a stout octavo of more than six hun- 

 dred pages, those who are at all familiar with natural history will 

 scarcely iieed to be told that the work of selection and compression 

 must hare been an arduous piece of business. 



?.laking due allowance for the acknowledged difficulties besetting 



