No. 2.] COMPARATIVE CYTOLOGICAL STUDIES. 271 



Lacaze-Duthiers ('54) finds in the eggs of Lamellibranclis 

 either one nucleolus, or when two are present they are of 

 unequal size. 



Leydig ('55a) says that in the egg of Cyclas "der Keimfieck 

 hat constant die Bisquitform." In a second paper of the same 

 year ('55b) he makes the following notes on the ova of Rotato- 

 ria : in Notommata ■niyrnteleo there are about 100 finely granu- 

 lated nucleoli ; in N. sicboldii " Die Keimflecke erscheinen 

 als Haufen von kleinen, hellen Kiigelchen," and disappear in 

 the ripe egg ; in N. ceiitrura and Brachionus bakeri there is a 

 single large nucleolus. 



Agassiz ('57) in studying the egg of the turtle introduces 

 the following terms: " ectoblast " for cell membrane, "meso- 

 blast" for nucleus, " entoblast," or "Wagnerian vesicle," for 

 the nucleolus, and " entosthoblast," or "Valentinian vesicle," 

 for the body sometimes enclosed in the latter. In the youngest 

 ova the nucleoli are absent, later they become numerous and 

 large, though they disappear in the ripe egg. The excentric 

 vacuole ("Valentinian vesicle") of the nucleolus "increases in 

 size at a greater proportionate rate than its parent, the 

 " Wagnerian vesicle," till at its final stage it oftentimes occupies 

 three-fifths of the diameter of the generating medium." 



Lacaze-Duthiers ('57), ovarian egg of Dentalimn : at first 

 there is but a single nucleolus, later a second one appears and 

 apposes itself to the former ; the volumes of the two are 

 different. {Cf. Fol, '89.) 



Remak ('58), blood cells of Callus: " Es kann kaum einem 

 Zweifel unterliegen, dass die Theilung der Blutzellen mit der 

 Theilung des Kernkorperchens beginnt. . . . Die Regel ist, 

 dass das Kernkorperchen sich in zwei Theile abschniirt, und 

 ebenso der Kern in zwei Kerne. Wie es aber zuweilen vier 

 Kernkorperchen giebt, so finden sich auch zuweilen vier Kerne 

 in einer Zelle." 



i86i-6g. 



Pfliiger ('63) found one nucleolus in the egg of the calf. 

 While in the " Urei " of the cat he makes the interesting 

 observation that after a division of the nucleus, whereby one 



