No. 4. — CONTRIBUTIONS FROM THE ZOOLOGICAL LABORATORY 

 OF THE MUSEUM OF COMPARATIVE ZOOLOGY AT HARVARD 

 COLLEGE, UNDER THE DIRECTION OF E. L. MARK, No. 194. 



Studies on the Nuclear Cycle of Gonionemus murbachii A. G. 

 Mayer. By Henry B. Bigelow. 



TABLE OF CONTENTS. 



I. Introduction 



II. Material and methods . . . 



III. Historical survey 



1. The somatic nucleus . . 



2. Spermatogenesis .... 



3. The oocyte nucleus . . . 



4. Maturation, fertilization, 



and early cleavage . . 



IV. Observations 



A. Mitosis in the somatic 



cells of adult tissues . 



B. Spermatogenesis . . . 



1. The spermatogonia 



Prophase . . . 

 Metaphase . . 

 Anaphase . . . 



2. The primary sper- 



matocytes . . . 



3. The first matura- 



tion division . 

 Prophase . . . 

 Metaphase . . 

 Anaphase . . . 

 Telophase . . . 



4. The secondary sper- 



matocytes . . 



5. The second matura- 



tion division . . 



6. The metamorpho- 



sis of the sper- 

 matid 



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325 



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7. Giant and multiple 

 spermatids and 



spermatozoa . . 333 



C. Oogenesis 335 



1. The oogonia ... 336 



2. The oocytes ... 341 



Pseudoprophase . 341 



Growth period . 346 



Staining reactions 350 



D. Fertilization 352 



E. The cleavage mitoses . 355 



1. The first cleavage . 356 



2. The second cleavage 357 



3. The third and sub- 



sequent cleavages 358 

 V. General discussion and con- 

 clusions 360 



1. The resting nucleus . . 360 



2. The nucleolus .... 362 



The oocyte nu- 

 cleolus . . . 365 



3. The chromatin structures 367 



a. The spermatogonia! 



chromosomes . . 367 



b. Numerical reduction 



of the chromosomes 



and synapsis . . . 368 



c. The pseudoprophase 



of the oocyte . . 373 



d. The chromosomes of 



the cleavage spindles 374 



