CONTENTS 



1012 



No. 1. MARCH 



Jacques LoEB. Heredity in heterogeneous hybrids. Nineteen figures 1 



David H. Tennent. The behavior of the chromosomes in cross-fertilized 



Echinoid eggs. Twenty figures 17 



Roy L. Moodie. The skull structure of Diplocaulus magnicornis Cope and 

 the amphibian order Diplocaulia. Seven figures 31 



Michael F. Guyer. Modifications in the testes of hybrids from the guinea and 



the common fowl. Twenty-three figures 45 



Bertram G. Smith. The embryology of Cryptobranchus allegheniensis, in- 

 cluding comparisons with some other vertebrates. I. Introduction: The 

 history of the egg before cleavage. Fifty-six figures 61 



Edwin G. Conklin. Body size and cell size. Twelve figures 159 



No. 2. JUNE 



Henry Leslie Osborn. On the structure of Clinostomum marginatum, a 

 trematode iiarasite of the frog, bass, and heron. Seventeen figures 189 



B. F. Kingsbury and Pauline Hirsh. The degenerations in the secondary 



spermatogonia of Desmognathus fusca. Twenty-one figures 231 



R. T. Young. The epithelium of Turbellaria. Six figures 255 



George W. Bartelmez. The bilaterality of the pigeon's egg. A study in egg 

 organization from the first growth i^eriod of the oocyte to the beginning 

 of cleavage. Forty-seven figures 269 



Fernandus Payne. I. A further study of the chromosomes of the Redu- 

 viidae. II. The nucleolus in the young oocytes and origin of the ova in 

 Gelastocoris. Ten figures 331 



iii 



