No. 2'.] COMPARATIVE CYTOLOGICAL STUDIES. 271 
Lacaze-Duthiers (’ 54 ) finds in the eggs of Lamellibranchs 
either one nucleolus, or when two are present they are of 
unequal size. 
Leydig (’ 55 a) says that in the egg of Cyclas “ der Keimfleck 
hat constant die Bisquitform.” In a second paper of the same 
year (’ 55 b) he makes the following notes on the ova of Rotato¬ 
ria: in Notommata myrmeleo there are about 100 finely granu¬ 
lated nucleoli ; in N. sieboldii “ Die Keimflecke erscheinen 
als Haufen von kleinen, hellen Kiigelchen,” and disappear in 
the ripe egg ; in N. centrara 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 Dentalium: 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 Galius: “ 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.” 
1861-69. 
PfUiger (’ 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 
