No. 4. — CONTRIBUTIONS FROM THE ZOOLOGICAL LABORATORY 

 OF THE MUSEUM OF COMPARATIVE ZOOLOGY AT HARVARD 

 COLLEGE, UNDER THE DIRECTION OF E. L. MARK, No. 157. 



The Maturation, Fertilization, and Early Cleavage of Haminea 



solitaria (Say). 



By W. M. Smallwood. 

 table of contents. 



PAGE 



I. Introduction 261 



II. Collection of Material and 



Technique 262 



III. Observations 264 



1. Growth of the Egg .... 264 



2. Maturation Clianges . . . 266 



(a) Before Deposition . . . 266 



Centrosome 266 



Cortical Layer .... 2G9 



Astral Rays 270 



Chromosomes .... 271 



(b) After Deposition .... 275 

 (I.) First Maturation Figure 275 



Centrosome .... 276 

 Cortical Layer . . . 279 

 Chromosomes . . . 280 

 (11.) Second Maturation Figure 281 

 (o) Direct or Shorter Pro- 

 cess 282 



PAGE 



(5) Longer Process . . 285 

 Chromosomes . . ". . 289 



Astral Rays 290 



Centrosome 291 



(c) Further Changes in Matu- 



ration 292 



(d) Literature and Discussion of 

 'Results 294 



Chromosomes 298 



3. Fertilization 299 



4. Early Cleavage 301 



(a) Metamorphosis of the Chro- 



matin 301 



(b) Origin and Fate of the 



Cleavage Asters .... 302 



(c) Discussion of Results and 



Literature 306 



5. Summary 309 



I. Introduction. 



During the summer of 1897, while at Wood's Hole, Dr. E. G. Conklin 

 suggested that I work up the natural history and development of Ha- 

 minea solitaria. The work has been carried on at Syracuse University, 

 at Wood's Hole, for three seasons, and, as opportunity offered, in connec- 

 tion with my work at Allegheny College. The study of maturation and 

 fertilization has been completed during the past year at the Zoological 

 Laboratory of Harvard University. 



I am under especial obligation to Dr. E. L. Mark for many helpful 

 criticisms. I have also received valuable suggestions from Drs. Conklin, 

 Hargitt, Lillie, and others. 



VOL. XLV. NO. 4 



