644 



SCIENCE. 



LN. S. Vol. V. No. 121. 



the single egg is transferred by the mother 

 to the temporary marsupium, where the 

 young are hatched, the period from fer- 

 tilization to hatching being about ten weeks. 

 OrnithorhyncJms, being an aquatic animal, 

 develops no marsupium, and the eggs are 

 said to be deposited in the burrow which 

 the animal constructs, but upon this point 

 Semon made no observations. 



Most of Semon's studies of the develop- 

 ment were upon Echidna. The Monotreme 

 egg is strictly telolecithal, resembling the 

 eggs of Sauropsids in many points. The 

 four-celled stage shows two vertical cleav- 

 ages at right angles, the blastomeres being 

 exactly equal. Quite early in development 

 the blastoderm is seen to consist of a layer, 

 one cell in thickness, except near the middle, 

 where a few cells lie deeper. These were 

 called hypoblast by Caldwell in 1887, but 

 Semon regards this apparently two-layered 

 stage as a morula, since he finds that the 

 blastoderm later resumes the one-layered 

 condition which he calls the blastula. In 

 the mode of gastrulation the Monoti'eme egg 

 suggests the Anamniotic type, the invagi- 

 nation preceding or accompanying the for- 

 mation of csenogenetic entoderm, instead of 

 following it as in Sauropsids and Mammals 

 generally. 



Late embryos of Echidna show external 

 genital knobs, which become enclosed within 

 the cloaca before the time of hatching. 



Among observations on the foetal mem- 

 branes may be mentioned the persistent 

 union of amnion and serosa (chorion), 

 which is very similar to the condition de- 

 scribed in Chelonia by Mitsukuri. During 

 the latter half of the embryonic period the 

 body lies between the allantois on the right 

 and the yolk-sac on the left, the two 

 structures being, for a time, of nearly equal 

 size. The inner walls of the allantois be- 

 come adherent, obliterating its cavity, ex- 

 cept near the middle, while the outer sur- 

 face, which is very vascular, unites with 



the chorion and serves undoubtedly as a re- 

 spiratory organ, as in Sauropsids. 



Some very interesting notes on the body 

 temperature are recorded, which show 

 that it bears no direct relation to season,, 

 age nor temperature of the external air. 

 Temperatures taken in the cloaca, varied 

 from 26.5° C. to 34° C, so that the Mono- 

 tremes are in a sense midway between the 

 so-called cold-blooded and warm-blooded 

 animals in regard to body temperature. 



J. H. McG. 



Columbia Univeesity. 



NOTES ON FRENCH GEOGBAPHT. 

 PAYS DE BRAY. 



The even skyline seen in looking across 

 from either side of the vallee de Bray between 

 Neufchatel and Bauvais, in northwestern 

 France, is a most marked feature in the 

 landscape. One rides over the even chalk 

 upland to come suddenly upon the crest of 

 an escarpment that descends steeply before 

 him. He there looks across a lowland and 

 sees a similar escarpment ascending upon 

 the farther side, whose elevation above sea- 

 level is about the same as that of the crest 

 upon which he stands. After descending 

 and crossing the different formations with 

 varying structures appropriate to the half 

 dome, cut off on the east by a series of 

 faults which is the main structure of the 

 Pays de Bray, he ascends the other side of 

 the lowland and finds himself again on a 

 Chalk upland exactly like that which he 

 left. One at first sight might suppose that 

 here is the uncovered base of a dome which 

 had been baseleveled and later covered by 

 horizontal Cretaceous beds. The exceed- 

 ingly level skyline lends countenance to 

 this view, but even a hasty inspection of 

 the region shows that this is not the case. 



The production of the even upland is 

 subsequent to the uplift of the half- dome, 

 which once must have risen higher than the 

 present upland. Two reasons for this are 



