BIFURCATION IN THE EMBRYOS OF TUBIFEX. 1 



PAUL S. WELCH. 



INTRODUCTION. 



In the course of some experiments upon one of the common 

 tubificids, Tubifex tubifex (Miill.), teratological phenomena were 

 discovered in the early development which merit attention. 

 Instances of bifurcation have been reported in collections of 

 mature and semi-mature Oligochseta from natural environments, 

 but always as great rarities and usually assumed to be the result 

 of regeneration following some form of injury. A considerable 

 number of bifid forms have also been produced in connection 

 with regeneration experiments. Bifurcation as an embryonic 

 phenomenon in Oligochseta has heretofore been known only from 

 six records. According to Kleinenberg (1879, p. 219) and 

 Vejdovsky (1888-1892, p. 250), Duges (1828) observed and 

 figured a double monster of "Lumbricus trapezoides," and Ratzel 

 and Warschawsky (1868) described a similar abnormality in 

 "L. agiicola." Kleinenberg (1878; 1879, pp. 216-219) found 

 bifurcating embryos not infrequent in the cocoons of "Lumbricus 

 trapezoides.'" Vejdovsky (1888-1892, p. 252) found two such 

 monsters in the cocoons of "Lumbricus terrestris," one instance 

 in "Allolobophora fcetida," and a large number in "Allolobophora 

 trapezoides." Korschelt (1904, pp. 257-258, PI. 13, fig. i) described 

 and figured a bifid embryo taken from a cocoon of "Allolobophora 

 subrubicunda." Weber (1917) studied the anatomy of twelve 

 double embryos of "Helodrilus caliginosus trapezoides" although 

 apparently others were found as indicated by the statement 

 (P- 34?) "Out of the 184 cocoons opened 57 contained only one 

 individual, 101 two, and 25 eggs in various cleavage stages and 

 I four embryos. Thirty-five of the 101 cases were in the form 

 of monsters." 



In order that the identity of the above-mentioned annelids be 

 understood it is necessary to consider the present status of some 



1 Contribution from the Zoological Laboratory, University of Michigan. 



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