688 
J. P. Munson 
of the more granulär cytoplasm outside. In this protoplasm, appearing at 
first view like homogeneous archoplasm, it is possible tosee, with the highest 
power, a distinct indication of very delicate, dosely packed striations. 
The central part of this centrosphere may be partly embedded in 
the indentation of the nueleus, as in fig. 76. It is possible that in cases 
like that shown in fig. 77, the sphere may be wholly imbedded in the 
stalk of protoplasm extending into the interior of the nueleus. 
In cases where the plane of the section does not coincide with this 
stalk, a circular area of homogeneous archoplasm occupies the eenter of 
the germinal vesiele; in which case the germinal vesicle looks, in section 
like a ring. The central mass of archoplasm, or let us sav homogeneous 
protoplasm is always, so far as I have seen, connected with the main 
ring outside the germinal vesicle, sometimes, however, onlv by a very 
slender string or stalk. 
It is possible that further investigation with methods of fbdng better 
suited to this egg, than those I have used may reveal the centrosome as 
a constant element of the cytoplasm of this egg. 
III. General Survey of the Literature. 
Origin Structure and Signiflcance of the Yolk Nueleus. 
It appears from the literature that the yolk nueleus is to be found 
in the eggs of representatives of all classes of animals. Yet it is by no 
means admitted to be universally present. Even in spiders, where it is 
most prominent, Balbiani (4) admitted, that in a number of species he 
found no trace of it. Yet he says: “I was fortunate enough to find the 
body in a great number of representatives of almost all classes of verte- 
brates and invertebrates”. 
Thompson (89) wrote of the yolk Nueleus in frog’s egg: “I have in 
general found it present, and think it more probable that it may be destined 
to form the external and larger corpuscles of the yolk”. 
Says Henneguy (32) : “Ce n’est que chez quelques animaux que 
je suis arrive ä trouver la vßsicule de Balbiani d’une maniere constante 
dans tous les jeunes ovules; chez d’autres, je n’ai pu l’observcr qu’excep- 
tionnellement; chez beaucoup enfin je n’ai pu la voir”. 
Of the yolk nueleus of spiders v. Wittich (98) said in 1849 : “Ob 
derselbe früher, gleichzeitig oder später als das Keimbläschen entsteht, 
wage ich nicht zu entscheiden. Immer sah ich sie übereinander, und zwar 
so, daß das Keimbläschen im fundus folliculi, jener zweite Körper aber 
seinem Halse zu gelagert ist”. 
