BIFURCATION IN EMBRYOS OF TUBIFEX. 1 95 



according to the following analysis, all of the types specified 

 being represented. It should be stated that this analysis is 

 based upon observations on the activities and external features 

 of the living anomalies. 



A. Either anterior or posterior extremity bifid 



1. Bifurcation simple 



a. Branches equal. 



b. Branches unequal. 



2. Bifurcation compound 



a. Plane of bifurcation 



(1) Secondary bifurcation in same plane as primary. 



(2) Secondary bifurcation at right angles to primary. 



b. Equality of bifurcation 



(1) Parts of primary bifurcation equal; secondary equal 

 or unequal. 



(2) Parts of primary bifurcation unequal, secondary 

 equal or unequal. 



B. Both anterior and posterior extremities bifid 



1. Primary bifurcations in same plane. 



2. Primary bifurcations in different planes. 



3. Either or both bifurcations compound. 



In the writer's records anterior bifurcation with normal 

 posterior end occurs about twice as frequently as a posterior 

 bifurcation with normal anterior end. Furthermore, individuals 

 with both ends bifid are almost as frequent as anterior ones. 

 One series of one hundred and ten records taken at random 

 shows the following proportions: forty-five anterior, twenty- 

 four posterior, and forty-one combined anterior and posterior 

 bifurcations. Other records yield somewhat similar results. 



In most instances the recognition of compound bifurcations 

 involved no difficulty. Occasionally, however, a specimen 

 appeared which seemed at first sight to be some form of tri- 

 furcation, but careful examination demonstrated that some at 

 least were really compound bifurcations; others, however, could 

 not be definitely classified by external examination. Compound 

 bifurcations are not uncommon and a considerable number were 

 observed during the progress of this work. 



