* 
No. 465.] GENITALIA OF LYMNEA. 677 
results, but the data presented 
in this paper seem hardly suffi- 
cient for this purpose, although 
some interesting features are 
brought out. 
In the foregoing remarks, nine 
species and two varieties have 
been discussed. In comparing the 
genitalia of these eleven forms, sev- 
eral notable facts are at once appar- 
ent. The length of the penis as 
compared with the penis-sac is ^ Ef MH 
Eben { Fic. 11.— Comparison of the length of 
st riking . The following table the penis with the penis-sac. a, stag- 
$ . alis; 6, mighelsi, c, lustris ; 
shows these relations (see Fig. rg Re 
II):— 
Comparative Length of Penis and Pents-sac. 
One fourth length. One half length. Three fourths length. ^ Longer. 
appressa mighelst emarginata auricularia 
Jugularis palustris 
reflexa 
catascopium 
desidiosa 
humilis 
megasoma ? 
There seems to be some difference in the number of penis 
retractor muscles attached to the penis-sac. In stagnalis and 
palustris there are two, with a muscle extending from these 
muscles to the penis. In emarginata, mighelsi, auricularia, 
reflexa, desidiosa, humilis, and catascopium there is but one 
retractor, in which is inserted the penis muscle. In auricularia 
there is but one penis-sac retractor and no muscle is attached to 
the penis. The prostate shows some differences, being fusiform 
in some species (viz., desidiosa, auricularia, mighelst, etc.) and 
cylindrical with an enlarged bulbous termination im the other 
i 7 : ! ries 
species (viz., stagnalis, emarginata). The uterus also va 
from ovate to pyriform. 
