July 6, 1883.) 



SCIENCE. 



11 



COMPOSITION OF THE MESODERM. 



Under the title ' Archiblast and parablast,' Wal- 

 deyer has published a long article [Arch, mikrosk. 

 anat., xxii. 1), in which he reviews chiefly His's views 

 concerning the origin of the connective tissue, blood- 

 vessels, etc. ; but he also considers several cognate 

 questions. 



His's investigations have been confined to verte- 

 brates, but he apparently believes that his view is 

 also applicable to invertebrates. Professor His dis- 

 tinguishes two distinct groups of tissues, — the archi- 

 blastic and parablastic. The former includes all the 

 epithelial, muscular, .and nervous tissues, comprising, 

 therefore, the glands, smooth muscles, and neuroglia: 

 the parablastic group comprises all the connective 

 tissues and blood, with which are counted the blood 

 and lymph vessels, and also the leucocytes. The 

 parablast arises beyond the embryonic area proper as 

 cells which grow into the embryonic region. These 

 cells arise, according to His, out of the granules of 

 the white yolk; these granules, from cells in the yolk; 

 which cells are immigrated leucocytes, that enter the 

 ovum while it is still in the follicle of the ovary. 



Waldeyer accepts this division, but he differs from 

 His mainly in two points, — first, in excluding the lin- 

 ing of the peritoneal cavity from the list of endothelia, 

 and therefore also from the parablast; second, in 

 ascribing a different origin to the parablastic cells. 

 (As regards the first point, there can be no rcison- 

 able doubt that His's account of the origin of the 

 membrane is erroneous: because, 1, the disappear- 

 ance of the original epithelium, and the new forma- 

 tion by leucocytes of an epithelium on top of it, was, 

 to the last degree, improbable, so that a gross error 

 of observation would be more probable; 2, His w.\s 

 unable to bring forward any definite observations in 

 his favor; 3, his conclusion was and has since been 

 contr.adieted by the direct observations of others. 

 Waldeyer has done good service in calling general 

 attention to these objections, but the matter can 

 hardly be considered new.) 



As regards the second point, we reproduce Wal- 

 deyer's own summary (p. 47). In the eggs of all 

 animals which have blood and connective tissue at 

 all, the segmentation of the egg does not continue 

 in the same manner up to the end; but one must 

 distinguish a primary and a secondary segmentation: 

 the first divides the egg, so far as it is capable of seg- 

 mentation, into a number of cells which are mature 

 for the formation of the tissue, and form the primary 

 germinal layers. A remainder of immature segmen- 

 tation-cells ( in holoblastic eggs), or of egg-protoplasm, 

 which has not assumed the cell-form (in meroblaslic 

 eggs), is left over. In either form, this remainder 

 does not directly enter into the germ-Layers as an 

 integral component, but undergoes first a further cell- 

 formation, — the secondary segmentation. From the 

 cells thus formed, the parts richer in protoplasm are 

 cut off, and make the primitive parabl.ast-cells; while 

 the part richer in yolk remains only to be used as 

 nutritive material. It will be seen that the essence of 

 Waldeyer's theory is, that a portion of the segmenting 



egg is retarded by the presence of yolk ; and so there 

 are some cells, or, in m^roblastic eggs, some proto- 

 plasm, whicli is laggard in development, and does not 

 directly enter into the primitive layers, but becomes 

 the parablast. 



The parablast is essentially identical with the mes- 

 enchyma of the brothers Hertwig, except that the 

 latter include the smooth muscles in the group. 

 Waldeyer endeavors to justify his theory of the origin 

 of these tissues from laggard cells, but it seems to 

 the reporter unsuccessfully. 



There is given also, p. 38-44, a discussion of the 

 relation of the yolk to cleavage, in which the views 

 advanced several years ago by Minot {Proc. Host. soc. 

 nat. hist., xix.) are brought forward anew, apparently 

 without knowledge of their previous publication by 

 another writer. In the discussion of the origin of 

 the parablast-cells, p. ',1-27, it appears that His's view 

 of their origin from the white yolk is definitely shown 

 to be untenable. Incidentally, emphasis is laid upon 

 the f.ict, that, in meroblastic eggs, the protoplasm of 

 the animal pole sends down processes into the yolk : 

 it is from these processes in the ' keimwall ' of birds' 

 eggs that the parablast-cells arise, according to Wal- 

 deyer. His article, as a whole, is chiefly a discussion 

 of the literature of his subject. C. S. Minot. 



THE ECLIPSE OF ISSS. 

 At the present time, when interest is chiefly 

 drawn toward the successes of the astronomers who 

 observed the eclipse of the sun month before last from 

 the small islands in the Pacific Ocean, the results of 

 the eclipse of May 17, 1882, obtained in Egypt, have 

 especial significance. These were briefly stated by 

 Dr. Schuster at a late meeting of the Royal astro- 

 nomical society. During the progress of the eclif)se 

 three photographic instruments were at work:^one 

 took photographs of the corona itself ; a second was 

 a photographic camera with a prism placed in 

 front of it, that is, a spectroscope without a collima- 

 tor; and the third was a complete spectroscope. 

 Photographs were obtained in all three instruments. 

 The direct photographs of the corona indicate its 

 variations from eclipse to eclipse, — a matter of much 

 importance in solar physics. If the photographs 

 taken during eclipses in the past twenty years are 

 compared with each other, it will be seen that the 

 corona varies in a regular way with the state of the 

 sun's surface, although there are irregular minor 

 changes. At the sun-spot minimum the corona is 

 much more regular than at the maximum. At the 

 minimum there is a large equatorial extension, and 

 near the solar poles a series of curved rays. At the 

 maximum there is practically no regularity at all: the 

 long streamers go up sometimes in one direction, and 

 sometimes in another; and this last year, near the 

 sun-spot m.'iximum, there was absolutely no symmetry 

 in the .appearance of the corona. The transparency 

 of the streamers was most striking. f)ne streamer 

 can sometimes be traced through another, showing 

 that the matter, whatever it is, must be very thin. 

 The rifts start from the solar surface in an entirely 



