742 



SCIENCE. 



[X. S. Vol. XXI. No. 541. 



ferentiation of the germ layers take place to 

 a certain extent. 



The author concluded from these results 

 that some at least of the material that goes to 

 form the embryo lies at first high up in the 

 upper hemisphere of the egg. In the light of 

 this conclusion it became necessary to examine 

 once more the early development, especially 

 the pregastrula stages, for no one has sus- 

 pected that the embryo-forming material lies 

 in the upper hemisphere and is transported to 

 the lower hemisphere hefore the lips of the 

 blastopore have appeared. 



Briefly, the author's examination showed 

 that throughout the early period of segmenta- 

 tion, the material of the upper hemisphere gets 

 pushed far out to the sides of the egg. This 

 is brought about largely by the development 

 of the enormous segmentation cavity. During 

 the later cleavage period- the yolk cells of the 

 lower hemisphere push upwards into the seg- 

 mentation cavity, almost obliterating it. This 

 upward movement of the cells in the interior 

 is compensated for by the moving downwards 

 below the equator of the outer layers of the 

 egg. In this way the embryo-forming ma- 

 terial is carried into the lower hemisphere. 

 Along its edge the lips of the blastopore de- 

 velop. The dorsal, lateral and ventral lips 

 roll over the yolk (or more accurately, the 

 yolk draws in beneath their advancing lips) 

 and the dorsal organs of the embryo (the em- 

 bryo in a narrower sense) appear over the 

 lower or yolk hemisphere of the egg. 



Rejuvenescence in Protozoa: Gary N. Cal- 

 kins. 



Since 1876 it has been generally assumed 

 that one eifect of conjugation is rejuvenes- 

 cence or renewal of vitality in both of the 

 ex-conjugants. This assumption has never 

 been proved experimentally. In his Para- 

 mceeium work, begun in 1901, the author al- 

 most had the proof, but allowed the oppor- 

 tunity for obtaining it to pass without real- 

 izing it at the time. In order to complete the 

 earlier work a new series of experiments with 

 Paramoecium was started on the last day of 

 February (190.^)). consisting of three different 

 lines, at present in about the fortieth genera- 



tion after conjugation. In his original ex- 

 periments the author found strong evidence 

 against the old view that both ex-conjugants 

 are rejuvenated. In twenty pairs which were 

 cultivated after separating from conjugation, 

 at least one individual of each pair invariably 

 died before many days, thus indicating an 

 incipient fertilization like that in metazoa. 

 This phenomenon will be given careful study 

 in the experiments now under way. 



Temperature and Muscle Fatigue: Frederic 

 S. Lee. 



Lolmiann has recently claimed that a cold- 

 blooded muscle on being heated to a mam- 

 malian temperature shows a course of fati^e 

 similar to that of mammalian muscle, and, on 

 the other hand, that a warm-blooded muscle 

 on being cooled fatigues like the muscles of 

 cold-blooded animals at a similar temperature. 

 The author was unable to confirm Lohmann's 

 results, and maintains his own previous con- 

 clusion that the contraction process of the 

 muscles of cold-blooded animals in the course 

 of fatigue becomes greatly slowed, while those 

 of warm-blooded animals show no such phe- 

 nomenon. The muscles of the frog and the 

 turtle show their characteristic method of fa- 

 tigue whatever the temperature. The muscles 

 of warm-blooded animals on being cooled and 

 then fatigued show either no slowing of the 

 contraction process or only a slight slowing. 

 The latter seems to be most pronounced in the 

 rodents, namely, the rabbit, mouse and rat. 



On Intraureteral Pressure and its Relation to 

 the Peristaltic Movements of the Ureter, 

 with demonstrations. Daniel R. Lucas. 

 (By invitation.) 



The author has observed that suction nor- 

 mally follows the peristaltic wave of the 

 ureter; at the same time a force is exerted on 

 the fluid in front of the wave. The force of 

 the peristaltic wave was seen to raise a column 

 of water of considerable height. Wlien the 

 ureter is acting normally, the pressure in the 

 pelvis of the kidney remains constantly nega- 

 tive, the anatomical arrangement of the pelvis 

 preventing collapse under negative pressure. 

 These facts indicate that the ureter functions, 

 to some extent at least, as an active agent in 



