138 
OTTO C. GLASER 
system is clearly fit. This however, does not tell us why elimina- 
tion should take place, nor whether either this or the complicated 
machinery to secure it are more than compromise responses to 
thfc biological problem, whatever it be, that lies' back of both. As 
long as the nematocysts were considered part of the organic 
make-up of eolids, a sufficient reason for their presence and behav- 
ior was found in their supposed utility; nor is the case necessarily 
altered by the demonstration that the nettles are visitors rather 
than natives in the bodies of these molluscs. There are many 
details also which seem to add force to the argument from utility. 
It is a fact that the nematocysts of eolids explode on coming into 
contact with sea water or a medium more dilute. It is natural to 
infer that they are neither more nor less effective when extruded 
from a Montagua, than they would have been had they exploded 
in the mother tissues of the Tubularia that made them. It is like- 
% wise true that the explosion of these borrowed nettles is accom- 
panied by sensations of pain if allowed to take place on a sensitive 
part of the body, between the fingers or on the tip of the tongue. 
Moreover eolids behave exactly as though a high degree of utility 
attached to the nettling organs. When stimulated, thermally or 
mechanically the nematocysts are extruded, and explode in great 
numbers. Grosvenor remarks : 
''No one can have witnessed the reaction of an Aeolid to various sti- 
muli . . . ^vithout being convinced that the cerata are used as a 
means of defence. The body is contracted, the head being often nearly 
telescoped into the trunk while the cerata are erected and waved about, 
especially in the direction of the foreign bod}^, and are often considerably 
extended. 
Under these circumstances Grosvenor nevertheless did not 
witness the actual extrusion of nematocysts. Cuenot ('07), in 
discussing the same subject, writes: 
''Lorsqu'on touche un Eolidien avec une baguette de verre, il prend 
aussitot une attitude particuliere; les papilles s'erigent, s'allongent et 
se tournent autant que possible vers le point lese, comme si elles s'orien- 
taient pour cribler I'ennemi de nematocystes; mais en realite, comme le 
dit tres justement Grosvenor, il y a tres peu ou meme pas du tout de 
