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 PEOGRESS OF MICROSCOPICAL SCIENCE. 



A Giant Gregarine. — We tave just received from M. Van Beneden 

 a copy of his memoir on tlie development of gregarines, in wlaicli the 

 structure of Gregarina gigantea is fully described and figured. The 

 pamphlet has reached us too late for any fuller notice at the present ; 

 but we shall dwell upon it more extensively in our nest issue. It 

 seems a most valuable addition to the literatui'e of the subject, and 

 it treats very fully upon the development of this very curious group. 

 The author dwells upon Professor Beale's views on development of 

 tissues. The work is published in the ' Bulletins de 1' Academic royale 

 de Belgique,' 2me serie, tome XXXI,, No. 5, 1871. 



Tlie Embryos of Calopterijx, Agrion, and Diplax. — One of the finest 

 and most advanced memoirs that we have seen on these subjects is that 

 just published in the ' Memoirs of the Peabody Academy,' by Mr. A. 

 S. Packard, jun. It is extremely elaborate. After dealing at length 

 with the subjects, the author thus sums up the characters : — Since the 

 observations on Diplax were made, and abstracts read at the meeting 

 at Burlington (August, 1867) of the American Association for the 

 Advancement of Science, and published in the ' American Naturalist ' 

 for February, 1868, and in the 'Proceedings of the Boston Society of 

 Natural History' (vol. xi.) for January 22nd, 1868, he has received, 

 through the kindness of Dr. Alexander Brandt, of St. Petersburg, his 

 admirable paper " On the Embryology of Agrion, Calopteryx,and certain 

 Hemiptera." Brandt's studies were directed chiefly to the development 

 of the embryonal membranes. His conclusions are : " 1st. Caloj^teryx 

 and Agrion are developed according to the type of the development as 

 shown by Metschnikow to exist in the Hemiptera, namely, the germ or 

 primitive band is internal to the yolk. 2nd. In those insects with an 

 internal germ we need to distinguish an embryonal membrane, which 

 is divided into a visceral and a parietal layer. 3rd. The visceral layer 

 (veiled or plaited layer of Metschnikow) does not become united with 

 the extremities, but enters, together with the parietal layer (amnion of 

 Metschnikow), into the formation of the yolk sac. 4th. The formation 

 of the yolk sac, together with the revolution or turning of the embryo 

 on its transverse axis, consists in an independent contraction of the 

 parietal layer of the embryonal membrane." As Mr. Packard's atten- 

 tion was directed to morphological points, he can only infer from the 

 few data given above that Diplax and Perithemis have the same 

 arrangement of the embryonal membranes, and that these membranes 

 later in the life of the embryo form the yolk sac, through the contrac- 

 tion of the parietal layer of the embryonal membrane, as in Agrion, 

 Calopteryx, and certain Hemiptera. As regards the changes of the 

 embryo after the rudiments of the appendages have appeared, they 

 seem in Diplax and Perithemis to be the same as in Calopteryx and 

 Agrion. The embryo of Diplax is much thicker and shorter, corre- 

 sponding to the shorter, more ovate egg. The attitude of the germ 

 during its turning in the egg is identical with that of Agrion and 



