TWINNING IN EARTHWORMS 33 



from pond and river mud by means of a sieve. Each 

 cocoon contains from one to fourteen eggs or embryos, 

 the average being about nine. The only avenue of 

 escape from the cocoon is through the two necks of 

 the latter. When temporary plugs in these necks are 

 removed the apertures are just wide enough for a normal 

 young worm to emerge. 



About 20 per cent of the cocoons examined showed 

 one or more double-headed or double-tailed worms, 

 only one, two, or three bifid worms being present in 

 each. The various types of dupUcity are classified by 

 Welch as follows : 



A. Either anterior or posterior extremity bifid 



I. Bifurcation simple 

 a) Branches equal 



h) Branches unequal 

 II. Bifurcation compound 



a) Plane of bifurcation 



(i) Secondary bifurcation in same plane as primary 

 (2) Secondary bifurcation at right angles to primary 



b) Equality of bifurcation 



(i) 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 



I. Primary bifurcations in same plane 



II. Primary bifurcations in different planes 

 HI. Either or both bifurcations compound 



It was further brought out that anterior bifurcations 

 with normal posterior end are about twice as numerous 

 as those with posterior bifurcation and normal anterior 

 end. Furthermore those with both ends bifurcated 



