March Ifi, 1883.] 



SCIENCE. 



181 



coucerning tlie origin of the primitive streak. In a 

 series of five chick-embryos, 5-8| hours incubation, 

 the first important development noted was in the en- 

 toderm, wliicli in the front part of the area pellucida 

 remains thin, while in the posterior part it is thickened, 

 until at the edge of the opaca behind it is five or six 

 layers of cells thick. In the next stage there is a 

 short primitive streak (but without its cephalic pro- 

 cess) within the area peUueida, and formed essentially 

 by the thickened outer germ-layer. The inner layer 

 now includes both mesodermic and entodermic ele- 

 ments, and does not correspond to the definite ento- 

 derm of later stages. Around the edge of the ger- 

 minal disc the upper layer bends over, and is united 

 with the inner layer; the bend marks the germinal 

 wall and later randwulst, which is thickened poste- 

 riorly, forming Koller's sichel, which is not a distinct 

 structure. The inner layer forms one mass with the 

 germinal wall, and it is probable that the latter fur- 

 nishes the cells to thicken the former. The thickening 

 of the inner layer may be best interpreted as a step 

 towards the formation of the mesoderm. Gasser also 

 reports in detail his observations on the goose and 

 dove. Unfortunately the memoir is without plates, 

 and contains no summary of the author's conclusions. 

 — (Arch. f. anat. 2^hj/siol.; anat. abtli., 1882, .359.) 

 c. s. M. [397 



Colors of feathers. — In continuation of previous 

 communications Dr. Hans Gadow discusses the colors 

 which are not the result of pigments : blues he con- 

 siders to be the result chiefly of a series of fine lines 

 on the walls of the prism cells ; greens as the result, 

 most often, of decomposition of light from a yellow 

 pigment; metallic feathers are considered to work on 

 the simple principle of a prism. — {Proc. zool. soc. 

 £on(Z., 1882, iii.) j. a. j. [398 



Notochord of maminals. — Strahl in the paper 

 above noticed showed that the neurenteric canal 

 appears in the anterior end of the primitive streak, 

 and that its wall is concerned in the formation of the 

 notochord. His observations refer to lizards. Lie- 

 berkiihn has found a canal in guinea-pig embryos, 

 which occupies a similar position, and leads to the 

 formation of the notochord {chorda dorsalis). Tliis 

 canal is, therefore, probably homologous with that 

 of lizards, although it is developed in the interior of 

 the mesoderm without connection with the ectoderm. 

 Lieberkiihn's views on the early development of 

 mammals may be svimmarized as follows : After the 

 completion of segmentation, fluid accumulates be- 

 tween the outer cell layer and the inner cells in such 

 manner that the latter finally mark out the embryonic 

 disk, which accordingly consists of the outside cov- 

 ering of flattened cells (ectoderm), and the inner 

 layers of round yolk cells (entoderm). The entoderm 

 then grows on all sides, and becomes thinner. The 

 flatlening-out of the ectoderm is evidently a rather 

 complicated process, which Lieberkiihn tries to eluci- 

 date, following Balfour {Comp. embryoL, ii. 181, 182). 

 Next appears the mesoderm, before tlie primitive 

 streak becomes visible. The cells of the middle layer 

 appear between the two primitive layers, at first at 

 the posterior end of the disk. They are certainly 

 derived in part from the ectoderm, and very proba- 

 bly in part also from the entoderm, since in the 

 region of the primitive streak the three layers are 

 not limited one from another. Yet at first the meso- 

 derm appears in the mole as a simple layer of cells 

 between ento- and ectoderm. The primitive streak 

 is a thickening of tlie mesoderm, and terminates 

 anteriorly in a special thickening known as the cepha- 



lic process. This appears in guinea-pigs on the thir- 

 teenth day. The mesoderm in the process is entirely 

 separated from the ectoderm, which rises in a slight 

 convexity over it. The passage of the adherent 

 (mesodermic) primitive streak to the free 'process' 

 is known as Hensen's knot, it being marked later by 

 a slight enlargement. The process grows forward;, 

 and at the time it reaches the dark edge of the disk 

 a longitudinal canal appears in the midst of it, short 

 at first, but rapidly elongating. The canal subse- 

 quently breaks through into the entoderm; the open- 

 ing gradually, but irregularly, extends the length of 

 the canal, which thus becomes, as it were, a trough 

 or furrow in the dorsal wall of the entoderm. The 

 cells of the canal are cylindrical and high; the fur- 

 row flattens out, and its wall then appears a constit- 

 uent part of the entoderm. This stage has been 

 seen by previous observers. By the time the canal is 

 opened about to the middle of the germinal disk, the 

 formation of the medullary groove begins. In the 

 next stage Hensen's knot is relatively nearer the pos- 

 terior end of the disk. The protovertebrae appear. 

 By the time there are four, the chordal canal contin- 

 ues to grow backward in the primitive streak in the 

 same manner as at first; but at the posterior end the 

 diilerentiation of the chorda no longer precedes, but 

 follows, that of the medulla and intestine. The man- 

 ner in which tlie notochord becomes finally separated 

 from the entoderm has been accurately described in 

 other publications. (The author's text and plates are 

 arranged in inexcusable confusion. Those who wish 

 to read the original are counselled to begin with a care 

 ful study of the explanation of the plates.) — {Arch, 

 anat.physiol.; anat. abth., 1882, 399.) c. s. M. [399 



Foetal envelopes of Chiroptera. — According to 

 Eobin, the foetal envelopes of the Phyllostomidae re- 

 semble rather those of the rodents than of other Chi- 

 roptera. — {Comptes rendus, Dec. 2(3, 1882.) c. s. m. 



[40O 



The evolution of deer-antlers, and atavism in 

 the hog-deer. — A pair of antlers of the hog-deer 

 (Axisporcinus) is described by J. Cockburn, in which 

 the left horn bears five tines. The first two are nor- 

 mal; the third is bent inward and backward; the 

 fourth and fifth correspond somewhat closely to the 

 ' roya! ' and ' sur- royal ' of the Wapiti ( Alces canaden- 

 sis). Caton's opinion that such unusual forms are 

 due to accident is not concurred in, the present and 

 other similar cases being explained by atavism. 



Garrod's law, according to which the typical antler 

 consists of a bifurcated beam, with a brow-antler near 

 the ,base, is set aside in favor of Dawkin's theorem, 

 which is recast in the following words: " The devel- 

 opment of the antlers of individual species of cervines 

 is a recapitulation of the history of the development 

 of antlers in the group." The typical or primeval 

 antler, according to Cockburn, is a simple spike, 

 "capable of extensive furcation, reduplication, arrest 

 and redundancy of growth in parts." An attempt is 

 made to explain the form of the antlers of various 

 species of deer according to this theory. — {Journ. 

 Asiat. soc. Bengal, li., 1882, 44.) f. w. t. [401 



Behavior of the American flying-squirrel in 

 confinement. — Mr. F. H. King, wlio kept three 

 young flying-squirrels (Sciuropterus volucella) in con- 

 finement for several months, gives an interesting ac- 

 count of their actions. Tliey were strictly nocturnal, 

 assuming an especially playful mood at 10.45 p.m. 

 and 3.30 a.m., which, in each case, lasted an hour or 

 more. When on the wing, and just prior to alighting, 

 the fore-limbs were made to vibrate a.s if in true fliglit. 

 One of the specimens, having broken a hind-leg, 



