A Comparative Study of the Structure and Origin 
of the Yolk Nucleus. 
By 
J. P. Mun8on. 
(Awarded the Walker First Prize by the Boston Society of Natural History.) 
With plates XXIX— XXXIY. 
Table of Contents. 
I. Introduction: — problems — material — methods — historical. 
II. Original Observations and Inferences: — the egg of the tor- 
toise — Interpretation and summary — the yolk nucleus of spider eggs — 
yolk nucleus (vitelline body) in the egg of Limulus — real nuclei in cyto- 
plasm — yolk nucleus in egg of pigeon — the frog’s egg — the cat’s 
egg — the yolk nucleus in egg of fish — the yolk nucleus in egg of crayfish. 
III. General Survey of the Litera tu re: — origin, structure and signi- 
ficance of yolk nucleus — degenerative processes — extrusion of nuclear 
material — Interpretation of observations. 
IV. General Summary: — meaning of the term — cells devoured by eggs — 
evidences of degeneration — karyolymph — metaplasm — distribution of 
metaplasm — the sphere an organic part of cytoplasm — vitelline body a 
centrosphere — yolk nucleus an aster — growth of cytoplasm — metaplasm 
as food — relation to germinal vesicle — seat of assimilation and growth — 
relation to latebra — derived from centrosome — evidence of structure — 
origin de novo — morphologieal and physiologieal center — explanation 
of Strange forms — compared with macronucleus — relation to nebenkern. 
Literature cited. 
Explanation of plates XXIX — XXXIV. 
I. Introduction. 
Problems: — The question as to the comparative structure and 
origin of the yolk nucleus involves several other problems: 1. Is the yolk 
nucleus a normal element of the egg cytoplasm, or is it associated with 
