SIGNIFICANCE OF LARVAL MANTLE OF FRESH-WATER MUSSELS. 
209 
Herbers accords with Faussek in considering the mushroom body to be a 
functionless organ, representing merely the remains of the larval mantle. He 
differs somewhat, however, in not attributing a functionless condition until a 
later period than Faussek, who considers that the nutritional function is lost with 
the formation of the mushroom body. Herbers’s view apparently seems the more 
rational. Undoubtedly the mushroom body plays a part in the destruction and 
absorption of the larval adductor muscle, for in preparations of Anodonta corpulenta it 
was not uncommon to find abundant remains of the disintegrated adductor fibers 
within the mushroom body, apparently being transformed into food. Without 
the intermediation of some such organ it 
would be difficult to understand how so 
large a group of tissue cells as make up 
the larval adductor could disintegrate 
without causing some fatal cytolytic re- 
sponse with the developing larva. 
It is only on the complete destruc- 
tion of the larval adductor, which occurs 
about the middle of the parasitic period 
and when an advanced development of 
the definitive mantle has taken place, com- 
pletely encircling the transformed larval 
mantle, that the pronounced “ mushroom 
stage” of the latter is reached. From 
each side the degenerated larval mantle, 
very much vacuolated and containing 
only a small amount of cell detritus, which 
probably represents the remains of the 
larval adductor, flows into and practically 
fills the mantle space, touching from 
each side and enveloping the foot. One 
might conclude that at about this time 
the functional character of the larval 
mantle is ended, and that henceforth the 
mushroom body is in reality purely an atrophied organ, serving no well-defined pur- 
pose, with the nutritional function being taken over by the definitive mantle. While 
during its early development the cells of the definitive mantle are formed in a single 
layer, yet during the close of the parasitic period there is a bunching of these cells 
at the edge of the valves and the formation of a noticeable mantle sinus, which 
would offer a ready explanation for transmission of nutriment from the mantle 
to the remainder of the definitive organs. 
Faussek, while attempting to explain the nutrition during the latter stages 
of parasitism, seemed inclined to the view that the enteric canal came forward 
as a nutritional organ, but was never able to convince himself of the validity of this 
interpretation. 
56197°— 23 2 
Fig. 4.— Mushroom stage of encysted A. corpulenta, showing 
progress of definitive mantle cells (d. m. c.) from edge of 
valve (below) and also from region of gill buds (above). 
m. b., mushroom body; g. b., gill bud. 
