BIFURCATION IN EMBRYOS OF TUBIFEX. 193 



emerging from one cocoon were often observed, the maximum 

 number noted being thirteen. Futhermore, there seems to be no 

 way of predicting where the sterile eggs will occur. Apparently 

 they do appear more frequently in the larger cocoons but are not 

 exclusively confined to them. After the development has pro- 

 gressed for two or three days it is usually possible to distinguish 

 eggs which will develop and those which will not since the latter 

 retain for a time their initial appearance thus offering distinct 

 contrast with the changing color and shape of the former. 



These sterile eggs have at least two possible fates: (i) They 

 seem to be consumed as food by the developing worms in the same 

 cocoon whenever one or more have been delayed in their escape. 

 Often every trace of such eggs is eventually obliterated. (2) 

 Sometimes all of the developing worms escape early, leaving 

 sterile eggs behind. Such cocoons soon swarm with microscopic 

 organisms which facilitate the dissolution and disappearance of 

 the contents. 



Possibly these sterile eggs have something to do with enabling 

 worms to live for long periods within the cocoon after completing 

 their embryonic development. However, instances were ob- 

 served where worms continued to live in that confinement long 

 after all the granular egg contents had disappeared. 



As mentioned before, the only avenues of escape from the 

 cocoons are the two necks. After the plugs are removed the 

 diameter of these necks is just sufficient to permit the average, 

 normally formed individual to squeeze through. Departures 

 from the normal body form, especially swellings or bifurcations, 

 constitute very effective barriers and since, as will be shown later, 

 abnormalities are common in Tubifex tubifex, many an individual 

 never reaches the outside world. At the proper time for emer- 

 gence, exploring movements, especially with the anterior end, are 

 exhibited and when the aperture is finally discovered, efforts 

 leading to escape are quickly exerted. Complete exit may require 

 several minutes, even the greater part of an hour under some 

 conditions. Exit seems to be more easily and more quickly made 

 when the cocoon is surrounded by mud or debris than when 

 deposited in water on the botton of a glass aquarium, this 



