ON A MONSTROSI1T OF THE COMMON EARTHWORM. 20;> 



openings into the common groove will each become 

 a mouth, and the single egg will thus produce two 

 worms." The two worms remain for some time con- 

 nected by their necks, but the connecting band 

 gradually becomes weaker and ultimately breaks, 

 leaving the two worms perfectly distinct. Although 

 this is the normal progress of events in Lumbricus 

 trapezoides, Kleinenberg points out that frequently 

 the uniting cord does not relax in time to be able 

 to be broken, or is too greatly developed, and thus 

 numerous monstrosities occur ; but as these have 

 always two mouths well separated, as well as two 

 ani, it will be seen that it will be quite impossible 

 for them to live. 



In the monstrosity of the common earthworm 

 which I have described, I consider it most probable 

 that during the early gastrula or blastosphere stage 

 a division has taken place in the posterior part 

 closely resembling that which gives rise to two 

 complete individuals from the ovum of L. trapezoides t 

 and that, as development has gone on, the two 

 posterior parts have lengthened, become segmented, 

 and each developed an anus. The resemblance is 

 further borne out by the fact that the two posterior 

 parts are attached by their sides, the ventral surface 

 of each part being continuous with that of the front 

 part of the body. This also holds good for other 

 specimens that I have been able to get descriptions 

 of. 



In the catalogue of the teratological specimens 

 in the Museum of the Royal College of Surgeons, 

 published in 1872, prep. No. 20 is marked: "An 

 earthworm with the posterior third of the body 

 symmetrically double. Presented by W. Clift, Esq., 

 1810." On inquiring concerning this specimen, Prof. 

 Charles Stewart, Conservator of the Museum, kindly 

 writes informing me that in it "the abnormal ends 

 are united by their sides : in other words, the con- 

 dition is as if the worm had been divided by a mid- 

 dorso-ventral plane." He further says that in 



