The Microscofjs. 261 



EXPLANATIOX OF ABBREVIATIONS IN THE FIGURES. 



Ec, Ectodei'inal poitiou of skin. 



C. mn., Circular muscle layer. 



L. mu., Longitudinal muscle layer. 



Br., Brain. 



Ph., Cavity of pharynx. 



C. ts., Connective tissue. 



Set. v., Ventral setae. 



Cav., Body cavity. 



Seg., Segmental organs. 



V. u., Ventral nerve cord. 



V. v., Sub-neural hlood vessel. 



Ep. g., Goblet cell or mucus cell i»f ectoderm. 



Cu., Cuticle. 



Ep., Epithelium of pit lodging seta. 



Set., Seta. 



S. mu.. Muscle of seta. 



Gl. nu.. Nucleus of gland cells. 



M. nu., Nucleus of muscle cell. 



Ep. nu., Nucleus of ciliated epithelium. 



Cil., Cilia of epithelium cells. 



M. ph. nu.. Nuclei of pharyngeal muscle. 



CYTOLOGY OR CELLULAR BIOLOGY. 



IX. — THE NUCLEUS AND NUCLEOLUS. 

 REV. A. M. KIRSCH, C. S. C. 



OF all the parts of the cell, the nucleus presents the greatest 

 difficulties to the investigator, not only on account of its 

 minuteness, but even more so on account of its being the seat 

 of that physiological activity, which is closely related to that 

 mysterious force in nature, the activity of which calls into exis- 

 tence new cells and also new individual plants or animals. When 

 Carnoy wrote the following words : " The germinative vesicle is 

 the nucleus of the egg," he seems to say that the study of em- 

 bryology presupposes the study of the nucleus. Embryology is 

 regarded as the foundation of all knowledge of organized beings, 

 and therefore it becomes at once apparent that the study of the 

 cell-nucleus is at the bottom of all biological science. The study 

 of the nucleus is difficult, and Carnoy, although devoting con- 



