SUMMARY OF CURRENT RESEARCHES. 15 



ovaries of normal frogs often display in winter very marked degenera- 

 tive processes, so that control observations are necessary during the 

 course of the experiments. He believes that the experiments of some 

 other authors (notably Pdster) are vitiated by ignorance of this fact, 

 for they overestimate the pathological effect. 



The author finds that the inflammatory process produces three types 

 of modification, the .one produced depending on the state of the eggs : — 



(1) Those large eggs which, though practically mature, have not been 

 shed at the right season, offer in winter little resistance to the caustic 

 reagent and rapidly degenerate, but the degenerating process differs in 

 no respect from that which is the ultimate normal fate of these eggs ; 



(2) Normal eggs of large or medium size are so modified as to display a 

 much thickened vitelline membrane which protects the egg-contents from 

 injury ; later the yolk is gradually absorbed by an unknown mechanism ; 



(3) The third type occurs in small eggs at any season of the year'; 

 in it the follicle-cells wander into the protoplasm, which only breaks up 

 after a long period of degeneration. In the first and second types, the 

 two poles of the eggs show a different relation to the follicular cells. 

 The degenerating eggs exercise a strong attraction upon the follicular 

 cells, which may enter the protoplasm, or may merely push the vitelline 

 membrane inwards. This attraction is entirely confined to the follicle- 

 cells, and does not affect the blood-cells or the elements of the other egg- 

 envelopes. Blood-vessels and blood-cells do not enter the egg until the 

 complete destruction of the yolk. The resistance offered by the egg to 

 injurious influences varies greatly, being greatest in young eggs, and 

 least in full-grown ones. 



Cleavage of the Egg of the Bony Pike.* — Dr. A.C. Eyclesheimer 

 calls attention to the discrepant observations on the cleavage of the 

 ovum of Lepidosteus osseus which Balfour, Parker, and Beard have de- 

 scribed as holoblastic, and Dean as meroblastic. Is the egg unlike any 

 other vertebrate egg, now cleaving in a holoblastic fashion, and again 

 following the meroblastic form ? Sections reveal a peculiar blastodisc, 

 closely resembling that of Amia, plus a conical elongation which ex- 

 tends beyond a plane passing through the equator of the egg, giving to 

 the finely granular blastodisc a pear-shaped outline. The author con- 

 cludes that the cleavage cannot be called holoblastic, but that it illus- 

 trates an intermediate type. 



Influence of Salt Solutions upon Eggs.f— Prof. T.H. Morgan finds 

 that sea-urchin eggs, whether fertilised or not, when placed for a short 

 time in sea-water to which 2 per cent, or less of sodium or magnesium 

 chloride has been added, and then returned to sea- water, show clear 

 spots in variable number and disposition. In prepared sections the 

 spots are represented by " stars " like those seen in karyokinesis, and 

 some of the stars have central specks like centrosomes. 



Unfertilised sea-urchin eggs may, under the influence of salt solutions, 

 show processes like cleavage, but the cleavage is not normal, nor 

 does it lead to development. The chromosomes are distributed through 

 the egg, apparently by the action of the stars, and the cleavage takes 



* Anat. Anzeig., xvi. (1899) pp. 529-36 (5 figs.). 



t Arch. Entwickmecb., viii. (1899) pp. 448-536 (5 pis.). See Amer. Nat, xxxiii. 

 (1899) pp. 825-6. 



