STRUCTURE OF DOUBLE MONSTERS IN THE EARTHWORM. 343 



is a great mass of muscular tissue attached by thin strands to 

 the body wall. This condition is exactly similar to that found 

 in single individuals. 



The sub-intestinal blood vessels are clearly visible (y.b.v.) in 

 their normal position between the alimentary tract and the nerve 

 cord. On each side of the muscular pharynx there lies a more 

 or less regular vessel (D.B.V.} which when traced to the point 

 of separation of the two members will be found to approach the 

 center and then one passes into one individual, the other into 

 the other, the vessel on the left side passing into the upper half, 

 the one on the right into the lower half. 



Though the other monster is formed by a coalescence of the 

 two members through one segment only, that union is complete 

 in every respect from body wall to pharynx. Fig. 5 is a longi- 

 tudinal section through No. 171 showing a portion of one of the 

 brain ganglia together with a small part of the nerve cord of 

 each of the individuals. A study of the successive sections will 

 show that the pharynx arises from a flattened portion which is 

 lined with the same kind of epithelial cells as the rest of the 

 digestive tract and which lies between the two members as indi- 

 cated in Fig. 2, Plate I. (w). The ventral cords are found to be 

 connected to the cerebral ganglia, of which there are two sets, 

 one on each side of the mouth opening, by means of commissures 

 as in No. 95. 



The setae, not shown in this figure, and the nephridae lie along 

 the same side of the body as the nerve cord. 



(b) Those in which the alimentary tracts have not become 

 united. Nos. 91, 92, 142 and 173 shown in Plate II as Figs. 

 6, 7, 8 and 9 illustrate this group. It will be noted that though 

 only one definite pair of segments appear to be fused in the first 

 three cases, there is in each instance an irregular mass of tissue 

 between the separated edges of the fused pair of segments. 

 Whether these masses are modified segments has not been deter- 

 mined. 



In all four instances the nerve cords are formed on the side 

 opposite the line of fusion. These cords are joined to the bi- 

 lobed brains in a manner very similar to that -found in No. 95 

 (Fig. 3). It is to be noted that the union of these individuals 



