CONTENTS 



No. 1. DECEMBER, 1921 



J. T. Patterson. The development of Paracopidosomopsis. Two text figures 

 and twelve plates (ninety figures) 1 



Caswell Grave. Amaroucium constellatum (Verrill). II. The structure 

 and organization of the tadpole larva. Four text figures and four plates 

 (eleven figures) 71 



Frank Helvestine, Jr. Amitosis in the ciliated cells of the gill filaments of 



Cyclas. Two plates (seven figures) 103 



D. H. Wexrich. The structure and division of Trichomonas muris (Har*:- 

 mann) . One text figure and four plates (thirty-six figures) 119 



No. 2. MARCH, 1922 



Alexander Petrunkevitch. The circulatory system and segmentation in 



Arachnida. Two text figures and two plates (seven figures) 157 



W. Harold Leigh-Sharpe. The comparative morphology of the secondary 

 sexual characters of elasmobranch fishes — the claspers, clasper siphons, and 

 clasper glands. Memoir III. Five figures 191 



W. Harold Leigh-Sharpe. The comparative morphology of the secondary 

 sexual characters of Holocephali and elasmobranch fishes — the claspers, 

 clasper siphons, and clasper glands. JNIemoirlV. Twentj- -two figures 199' 



W. Harold Leigh-Sharpe. The comparative morphology of the secondary 

 sexual characters of Holocephail and elasmobranch fishes — the claspers, 

 clasper siphons, and clasper glands. Memoir V. Nineteen figures 221 



Walter N. Hess. Origin and development of the light-organs of Photurus 



pennsylvanica De Geer. Five plates (seventeen figures) 245 



Saxte Xaccarati. Contribution to the morphologic study of the thyreoid 



gland in Emys europaea. Two plates (five colored figures) 279 



Charles Eugexe Johnson. Branchial derivative in turtles. Five plates 



(twenty-four figures) 299 



Horace W. Stl'Nkard. Primary neuromeres and head segmentation. Twenty 

 figures 331 



No. 3. JUNE, 1922 



Bertram G. Smith. The origin of bilateral symmetry in the embiyo of 



Crypt obranchus allegheniensis. Thirty-three figures 357' 



Edith Pinney. The initial block to normal development in cross-fertilized 

 eggs. I. Crosses with the egg of Fundulus. II. Reciprocal crosses be- 

 tween Ctenolabrus and Prionotus. Two plates (seventeen figures) 401 



111 



n ^M 



