MONTGOMERY. 
266 
[VOL. XV. 
PAGE 
19. Gland cells of Piscicola rapax (Verr.). 483 
20. Mesenchym Cells of Cerebratulus lacteus (Verr.). 494 
21. Ganglion Cells of Nemerteans. 49^ 
IV. General Comparisons and Conclusions . 497 
Appendix to the Literature Reviews . 539 
Literature List. 542 
Explanation of Plates . 561 
I. INTRODUCTION. 
The following studies are based upon animal cells, both egg 
cells and somatic cells having been investigated. They were 
made, primarily, with a regard to the morphology of the true 
nucleoli (plasmosomes), though numerous other points in onto¬ 
genetic cellular development have been considered. In con¬ 
nection with these observations the zoological literature upon 
the subject of nucleoli has been reviewed as thoroughly as 
possible, and, less completely, the literature from the botan¬ 
ical standpoint as well; reviews are given of these observa¬ 
tions of previous writers. No attempt has been made to 
review the literature from the pathological standpoint. Under 
the caption “ General Comparisons and Conclusions ” are com¬ 
pared together the more important deductions from my own 
observations, and these are compared with those of previous 
investigators. 
The nucleoli are cellular structures which have been studied 
to much less extent than other constituents of the cell, and 
though there are numerous observations upon them, these are 
so scattered through works of more general import that it is 
well-nigh impossible to collect together all the previous inves¬ 
tigations upon the subject. I hope that this explanation may 
be taken as an apology by any authors whose papers I have 
chanced to overlook. 
At the laboratory of the Fish Commission at Woods Holl, 
the following species were collected by me : Montagna , Amphi- 
porus glntinosus, Tetrastemma catennlatum y Zygonemertes , 
Linens , Polydora , and Piscicola. At Sea Isle City, at the labo¬ 
ratory of the University of Pennsylvania : Tetrastemma elegans y 
DotOy and certain of the species found at the former locality. 
Stic hostemma was collected in the aquaria of the University 
