INVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 589 



traverses the embryonic nucleus and abuts peripherally at a point 

 where the first meridional groove will appear ; in other words, the 

 upper or active pole is disi:)laced. 



2. The nucleus undergoes transfoimations comparable to those 

 observed in the egg of most organisms (cleavage-amphiaster ). There 

 are three principal phases, to the last only of which the descriptions 

 and figures of Goette apply ; so that the egg-nucleus of Amphibians 

 makes no exception to the general rule. 



3. As Goette has shown, a clear rim, which I call cleavage plate, 

 precedes the appearance of the peripheric groove. It is most clearly 

 indicated in the plane of the future equatorial cleavage, thus esta- 

 blishing a marked separation between the ectodermic spherules and 

 the endodermic mass. It has manifestly for its seat the line of 

 separation between what I term the ectodermic and endodermic ex- 

 tremities of the egg. 



4. The meridional grooves arise as pale, strongly marked gutters 

 along the pigmentary cap of the upper hemisphere ; afterwards, by 

 effacement of the cleavage-spherules, the gutter becomes a simple 

 groove. The i:)igmentary line of separation then belongs, at least for 

 the most part, to the cortical layer. 



5. In the endodermic extremity, the meridional divisions increase 

 in activity from the centre towards the periphery. Accordingly, at 

 any given moment, the cleft portion covers a still undivided region, 

 represented in sections by an ellipse whose base corresponds to the 

 lower pole of the egg. 



6. Certain phenomena, such as the impulsion of cortical pigmen- 

 tary masses towards the interior of the egg, the irregularities in the 

 planes of division observable in some phases, &c., arc explicable only 

 by admitting the existence of contractions of the protoplasm of the 

 egg dui'ing cleavage. 



7. The roof of the segmentation-cavity, at first monoderic, be- 

 comes polyderic. There is here no diiierence between the eggs of 

 Anoura and Urodela. 



Vital Properties of Cells.* — M. Eanvier directs particular atten- 

 tion to the appearance of nuclei in dead cells ; taking for example 

 the lympliatic and " fixed " cells of the cornea, he points out that, 

 during life, no nuclei can be made out in them, but that these appear 

 after the death of the cells. The reason of this appears to bo that, 

 during life, the nuclei are not apparent because their refractive 

 power is very much the same as that of the surrounding protoplasm. 

 At death, changes take place in the protoplasm, so that they then 

 become apparent. In illustration of this ho has performed the 

 following experiments : — - 



(1) Two corneae were carefully removed from a frog, and were 

 both placed in damp chambers, exactly similar in construction ; one, 

 in a room of 23^, was submitted for ten seconds to the action of an 

 electric current ; this was sufficient to kill some of the cells, and their 

 nuclei became apparent two minutes afterwards. The other was 



♦ ' Comptos Rori'liiH.' Ixxxix. (187^) p. .S18. 



