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. 1 88
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