OBSERVATIONS ON THE STRUCTURE OF DOUBLE 

 MONSTERS IN THE EARTHWORM. 1 



ROXIE A. WEBER. 



I. INTRODUCTION. 



The work which has thus far been done on double monsters 

 in the terricolous group of annelids is quite limited, since in 

 only a few species, Lumbricus trapezoides, Lumbricus terrestris, 

 Allolobophora fcetida and Allolobophora trapezoides, has this con- 

 dition been observed. The first of these forms is described by 

 Kleinenberg, the remaining three by Vedjovsky. These two 

 investigators agree neither as to the method of union nor as to 

 the cause of this phenomenon. It is not the object of this paper 

 to give the factors influencing such monster formations, but 

 merely to describe the manner in which the members are joined. 



Material and Technique. The material studied consists of 

 twelve double embryos, the shortest member of which is at least 

 60 segments in length, the longest 125, one monster in which 

 one individual consists of 16 the other 17 segments, 19 double 

 gastrulae and two embryos showing a bud on one side of the 

 blastopore, and one case of an egg consisting of two distinct 

 hemispheres connected by a band of large cells. The entire 

 supply was obtained from Professor Patterson, of this University. 



The fixing fluids employed were Meves, Gilson, and Bouin, 

 all of which gave only fairly good results. Ehrlich's haematoxylin 

 was used as a stain. 



The species studied is Helodrilus caliginosus trapezoides, ac- 

 , cording to Professor F. Smith's identification. 



Review of the Literature. Before describing the individuals 

 studied, it will perhaps be well to give a brief review of the 

 results of the two authors above mentioned. 



Kleinenberg found that the number of eggs in the capsules of 

 L. trapezoides varies from three to eight of which usually one, 



1 Contributions from the Zoological Laboratory of The University of Texas, 

 No. 139. 



339 



