1883.] NATURAL SCIENCES OF PHILADELPHIA. 233 



epidermis. When the eyes are retracted (for they can be retracted 

 in these animals) they lie close to this pair of ganglia. 



In A. Jluviatilis the eyes and ganglia nre seen in the same trans- 

 verse sections (PI. X, fig. 8). This is not the case in A. lacustris, 

 as the ganglia lie a little posterior to the retracted eyes. Each 

 ganglion of this pair lies at the base of a tentacle, and each is ovoid 

 in shape, the longer axis being ante ro- posteriorly situated. They 

 are covered with a fine tunica of connective tissue. The nerve 

 that snpplies them comes from the cerebral ganglia and enters this 

 ganglion on its inner surface. The nerve-cells which make up the 

 ganglia are in ever}' respect similar to those already described for 

 other ganglia. 



The tissue of the ganglia is pierced by a bundle of muscular 

 fibres (PI. X, fig. 7 rw), which comes from the buccal mass, 

 pierces each ganglion and is inserted in that part of the epidermis 

 which is covered by the ganglion. This muscle was not observed 

 by Sarasin.i When this muscle contracts, the epidermis, together 

 with the ganglion, is drawn inward. 



The figures T and 8 (PI. X) represent two transverse sections 

 through the ganglion of the left side of J. Jiuxnatilis. In fig. 1 

 we see this most anterior of tlie two sections representing the 

 retractor muscle. Fig. 8 shows the relation of the ganglion to 

 the eye. In these two sections we see that the ganglion has a 

 deep groove on its external surface, so that in fig. 7 we have a 

 figure somewhat resembling that of the ganglion olfactorium (PI. 

 X, fig. 6 Go). 



This groove, /* (PI. X, fig. 7), is caused by the contraction of 

 the retractor muscle. This groove was always present in sections. 



In the figui'e 7, the nerve (n) which comes from the cerebral 

 ganglion is seen entering the ganglion in question. At that point 

 where the ganglion comes in contact with the cells of the epider- 

 mis (p)', they seem to be somewhat longer than those surrounding 

 this part. When the surface of this part is viewed from the exterior 

 a pale patch is seen, which is made up of these lengthened epi- 

 dermal cells. The external surface of these cells is covered with 

 cilia which are a trifle longer than those found on the adjoining 

 epithelium. Sarasin^ considers this pair of ganglia as a special 

 organ of sense ; I am inclined to believe that we have here an 



^ Drei Sinnesorgane, etc. 



^ Ueber drei Sinnesorgane, etc. 



16 



