258 Annals Entomological Society of America [Vol. XV, 



mesothoracic ganglia are about the same size as the sub-cesophageal 

 ganglion and are each situated equidistantly from the anterior and 

 posterior margins of the segments and this condition prevails for the 

 three species. The meta thoracic ganglion is larger than those of the 

 preceding segments and its position is not the same in the different 

 species for it is here that the thoracic fusion point occurs. In Phryganea 

 interrupta the ganglion is centrally located with the ganglion of the 

 first abdominal segment just within the posterior border of the meta- 

 thorax. In Limnophilus indivisus, the metathoracic ganglion has 

 migrated forward and the first abdominal ganglion has followed until 

 the latter occupies the central position with the metathoracic ganglion 

 well in the front half of the segment. In Hydropsychodes analis, the 

 condition is the same as in L. indivisus. 



In the abdomen of the three species the positions of the ganglia 

 are more noticeably variable. In P. interrupta the first abdominal 

 segment bears at its posterior margin, the ganglion of segment two 

 and segment two is void of any ganglion, but receiving its innervation 

 from its respective ganglion located in segment one. The ganglia of 

 segments three, four, five and six occur in their respective segments 

 near the front margins. Segment seven bears in its front half, two 

 ganglia; these are the ganglia for segments seven and eight and they 

 are very closely united, but not fused at all, Plate XIV, Fig. 2. In 

 L. indivisus, the ganglion of segment two occupies a central position 

 in segment one, indicating a forward migration. Segments three, four 

 and five have their ganglia in the front half of the segment as in P. 

 interrupta. In segment six all the ganglia of the three segments, six, 

 seven and eight, are placed; those relating to segments seven and eight 

 are closely united, practically fused, and take a position in the posterior 

 half of the segment. The ganglion for segment six is in the anterior 

 half of the segment, Plate XIV, Fig. 1. In H. analis we find an arrange- 

 ment in the abdomen which varies from that which Pictet, 1834, 

 observed in Hy dropsy che, for he saw all the ganglia here upon the 

 divisions between the segments. In this particular species, the ganglion 

 for segment two is in segment one as usual, and the ganglion for segment 

 three is on the margin between segments two and three which is a 

 forward migration. The ganglion for segment four is in front of the 

 center of the segment and the ganglion for segment five is back of the 

 center of its respective segment. In the sixth abdominal segment 

 are three ganglia, for segments six, seven and eight respectively and all 

 are in a line and practically fused, Plate XIV, Fig. 3. 



The thoracic ganglia and the abdominal from one to six innervate 

 their respective _segments and appendages, the seventh abdominal 

 appears to have only one pair of nerves which extend backward into 

 segment seven, the eighth abdominal ganglion innervates segment 

 eight and nine, as well as the swimmerets. which extend out from seg- 

 ment nine. There are various ways for the eighth abdominal segment 

 to innervate segment nine. In P. interrupta and H. analis it sends a 

 nerve directly to the segment, but in L. indivisus the nerve which 

 extends to segment eight branches and sends a branch to segment 



