Habits and structure of Cotylaspis insignis Leıpy. 207 
positions. In the evening of that day they were found to be 
approaching each other, and on the following morning forty-eight 
hours after the beginning of the experiment they had left the kidney 
which was dead and decaying and moved to the adjoining surface 
of the visceral mass. 
Removed to glass dishes and kept covered to protect them from 
dust, in either hydrant water or a mixture of half normal salt 
solution and half hydrant water, equal parts, they will live three 
weeks or more. They then adhere constantly to a certain spot and 
keep going through the motions just described, thereby keeping 
the area around them swept perfectly clean. 
Most of the Aspidobothridae are strictly parasitic. Aspidogaster 
conchicola inhabits the kidney and pericardial cavity of different 
Unionidae, A. limacoides, the intestine of Leuciscus of Europe, Lopho- 
taspis (Aspidogaster) vallei, the stomach of Thalassochelys, a turtle, 
Cotylogaster lives in the intestine of fishes, Macraspis and Sticho- 
cotyle are from biliary organs of fishes, Cotylaspis lenoiri inhabits the 
intestine of a turtle. C. insignis is unlike all of these in living on 
the outer surface of its host, and unlike most in having an inverte- 
brate host. While it is generally spoken of as a parasite, it can 
hardly be considered even ecto-parasitic but is more strictly 
commensal since it not only does not draw any nutriment from its 
host but is even a benefit to it by keeping the surface of the 
kidney free from organic material, in which we can readily suppose in- 
jurious organisms might find lodgment. The almost free habit of 
C. insignis would seem to be secondary and arrived at by way of a 
partially free ancestral form such having habits like those of 
Aspidogaster. 
While looking through Unionidae for C. insignis the pericardial and 
kidney cavities were also opened and examined, in several hundred 
cases; in no case did C. insignis occur in these cavities. Its habit 
in this respect is in marked contrast with A. conchicola. It also 
resulted from these studies that we now know that A. conchicola is 
not a member of the fauna of Lake Chautauqua, or if it does occur 
there is extremely rare. 
d) External anatomy. 
The total length of C. insignis from 36 preserved individuals was 
found to range between 1.2 mm and 1.8 mm, the width between 
0.6 mm and 1.0mm. Lerpy (1858) gave the length as '/, to 1 line, 
