342 ROXIE A. WEBER. 



digestive tract is either fused or not fused, but the nervous system 

 is modified in a variety of ways. The manner and extent of 

 union of these individuals and their organ systems are best 

 described in the following groups. 



i. Those double monsters in which the union is dorsal. This 

 group may again be subdivided into 



(a) Those in which the union extends to the alimentary 

 tracts. Of these there are two examples, Nos. 95 and 171, 

 Plate I. From Figs, i and 2, Plate I., it can be seen that the 

 fusion in No. 171 is through one segment only, while in No. 95 

 it extends through five. A description of sections through this 

 monster will serve to show the general relationship of the organ 

 systems in the members of this group. Fig. 3, Plate I., is a 

 section through the anterior portion showing the condition of 

 the nervous system. It will be seen that there is almost a con- 

 tinuous band of nerve tissue extending around the pharynx. A 

 study of the neighboring sections shows that this band is really 

 complete. It will also show that the portion marked (6) in the 

 figure enlarges into a bilobed brain and that a similar structure 

 exists on the opposite side of the pharynx. At the same time 

 there is also to be found at each end of the greatly elongated 

 pharynx another set of ganglia. It would be impossible here to 

 determine which are brain and which are ventral cord ganglia 

 were it not for the presence of setae (s). This at once leads to 

 the conclusion that the ganglia at the end of the pharynx must 

 be those of the ventral cord. This inference is further proven 

 by a study of sections through a more posterior region, as shown 

 in Fig. 4, Plate I. Here are no longer to be found the ganglia 

 on either side of the pharynx but only those at the opposite ends. 

 This section too shows the setae in normal relationship with the 

 ventral cord and the nephridae in their natural position. They 

 are shown only on one side but those of the other half can be 

 seen in the next section. 



It will be noted that the single pharynx is greatly elongated 

 from end to end of the monster. Throughout the fused part it 

 remains as one cavity dividing into two parts only when the 

 point of separation of the two members is reached, one passing 

 into each individual. Surrounding the pharyngeal cavity there 



