1865.] Hlncks on Zoophytes : the History of their Development. 401 



finding it to yield eighteen lines instead of eleven. They also point 

 out that some of Kirchhoff's lines are incorrectly mapped. The 

 caesium was prepared with the greatest care by precipitation from 

 bitartrate of cassium, with bichloride of platinum. 



Professor Gibbs' Spectroscope. — ' Silliman's Journal,' No. CIIL, for 

 1863. — In this instrument, the prism has a refracting angle of only 

 37°. The rays fall on the first surface perpendicularly, and escape 

 almost parallel to the second. The dispersion is very great, while the 

 loss by reflection at the first surface in prisms of 60°, placed at the 

 angle of minimum deviation, is avoided. Though the telescopes 

 are only of 6 inches focal length, with a magnifying power of 6, it 

 compares favourably with a large apparatus of 18 inches focal 

 length, and 1^ inch aperture. This form of prism was first em- 

 ployed by Mathiessen, and if the first surface is made concave, so as 

 to admit the addition of a double convex of crown, it would present 

 great advantages in consequence of the saving of light. 



ZOOPHYTES: THE HISTOEY OF THEIR DEVELOPMENT. 



By the Rev. Thomas Hincks, B.A. 



The remarkable facts which have been brought to light of late years 

 respecting the reproduction of the Hydroid Zoophytes, — an Order of 

 compound, plant-like animals, chiefly marine, of which the Hydra is 

 the type, — facts which at first sight seemed little short of marvellous, 

 and of which we have had so many speculative interpretations, have 

 attracted notice even beyond the ranks of professed naturalists, and 

 have formed the staple of many a scientific romance in the pages of 

 our popular literature. Many who have but a smattering of zoological 

 knowledge will have heard the story, that certain Zoophytes produce 

 offspring totally unlike themselves — beings of dissimilar structure and 

 habit, and that these reproduce the likeness of the original stock ; they 

 will have read with wonder, how the stationary, plant-like animal gives 

 birth to a mercurial brood of restless rovers, and that there is a close 

 blood-relationship between the polype and the Medusa. The cele- 

 brated theory of the " alternation of generations" may also have 

 interested them as a curious speculation. But as yet the popular 

 apprehension of the whole subject is probably of the vaguest and 

 most inaccurate. It takes the form of a general notion that there are 

 creatures which have not a feature of resemblance to their own fathers 

 or mothers, nor yet to their own children, but which do resemble their 

 grandfathers and grandmothers, which exhibit, in short, a complete re- 

 versal of the ordinary laws of kindred. The story as thus rendered 

 has certainly enough of marvel and mystery about it to fascinate the 

 mind ; but we venture to think that the simple truth of Nature, as now 

 placed before us, through the concurrent labours of many observers, 

 is not less attractive, and we propose, apart from all technicalities, to 



VOL. II. 2 F 



