BIFURCATION IN EMBRYOS OF TUBIFEX. 1 9! 



Ordinarily, cocoons were carried through their development 

 in the laboratory by merely transfeiring them to shallow dishes 

 containing river or pond watei . For convenience of examination 

 such water was sometimes filtered, although this procedure is 

 not always necessary since the finely divided matter will usually 

 settle and has the advantage of serving as food material for the 

 young worms aftei they emerge. Occasionally mould attacked 

 the cocoons but its appearance was not frequent enough to 

 offer serious difficulty. 



THE COCOON. 



Dixon (1915, pp. 85-86) has described briefly the cocoon of 

 "Tubijex rivulomm," a form now regarded as identical with 

 Tubijex tubifex. In practically all respects this description has 

 been found correct. However, the color of the cocoons demands 

 comment. Dixon describes them as "Whitish or greyish in 

 colour and semi-transparent, but when viewed with the naked 

 eye they appear opaque, but this is due to the eggs which they 

 contain." In this work it has been found that the external 

 appearance depends somewhat upon the degree of development 

 of the eggs within. When first deposited they may have a 

 whitish or creamy tinge but as development proceeds there is an 

 increasing amount of yellow or orange, the maximum intensity 

 being reached at the time when the young worms are ready to 

 escape. At all stages the cocoon proper (the surrounding 

 capsule) is colorless and transparent. 



Excluding occasional malformed cocoons, the shape varies 

 from ovoid to sub-spherical with two symmetrically formed, 

 cylindrical, projecting necks, one at each end of the major axis. 

 These necks bear an important relation to certain matteis 

 considered in this paper since they are the exclusive avenues of 

 escape for the young worms. At the time of deposition these 

 necks are completely filled by plugs of mateiial somewhat 

 similar in appearance to the remainder of the cocoon but dis- 

 tinctly less resistant since they are easily penetrated at the proper 

 time, while in the hundreds of cocoons examined not a single one 

 had been punctured or ruptured elsewhere although they were 

 often subjected to considerable pressure by developing worms 



