208 
BULLETIN OF THE BUREAU OF FISHERIES. 
milk, with the carnivores the constituents of the blood, and in all these cases 
the embryos have a like parasitical relation to the mother that the developing 
glochidium has to its fish host. 
During this first encystment stage, as observed with Anodonta corpulenta, there 
has not been a very extensive development of the definitive organs. The lateral 
pits have increased in size and are beginning to show the ridges that give rise to 
the first pair of gill buds. The endoderm sac has developed lateral evaginations 
which represent the liver sacks. The foot fold has been given prominence, and 
the mantle cells, although still having an intracellular nutritional function, have 
fused into a solid layer with no discernible cell boundaries. The larval adductor 
muscle has remained unchanged. 
FORMATION OF “MUSHROOM BODY.” 
Following this there is the condition which Herbers calls “the stage with the 
ring of mantle cells,” which is conceded to be brought about by a mechanical process. 
The gill buds, which develop at this time from the lateral pits, cause the mantle cells 
to recede from the region of the body proper, so that they are confined more to 
the edges of the valves, which gives rise to Herbers designation. With the begin- 
ning of this stage, the r6le of the larval mantle as a nutritional organ is supposedly 
ended, the intracellular method of nutrition which it has been exhibiting dis- 
appearing as a result. Due to the formation of gill buds, the mantle cells are 
pushed away from the neighborhood of the foot fold, and coincident with this is 
the appearance from the edges of the valves of the cells of the definitive mantle, 
which ultimately supplants the larval mantle. The cells of the definitive mantle 
are short, cylindrical, and with smaller, more deeply stained nuclei than the' larval 
mantle cells, and the conspicuous nucleoli are absent. They are thus readily 
distinguished from the larval mantle, for whose destruction they are held so largely 
responsible. Herbers also records for Anodonta cellensis the formation of definitive 
mantle cells from the body proper, so that the larval mantle folds of the two valves 
become separated and are confined to the central portion of each valve (figs. 4 
and 9), w r here they project into the mantle cavity and give rise to what Braun, 
who first described it, called the “ Pilzf ormiger Korper ” or “mushroom body,” 
naming it for its peculiar mushroom resemblance. 
According to Faussek, Braun held this body to be a provisional nutritional 
organ of the larva, giving it the function of dissolving and absorbing the lime 
salts of the bony skin fold of the fin of the fish. Schmidt at a later date agreed 
wdth Braun, saying, quoting from Faussek, “die von Parasiten erfassten Teile des 
Flossenskelets stets ganzlich zerfallen und dass im Protoplasma der Zellen des 
‘ Pilzformigen Korpers’ verschiedener grosse Korperchen, die vollstandig des 
Zerfallsprodukten gleichen, nachweisbar sind.” Faussek, as a result of his own 
work, concluded that both Braun and Schmidt had only partially solved the ques- 
tion and considered the mushroom body to be merely the atrophied remains of 
the larval mantle, and as the real nutritional organ he held the layer of definitive 
mantle cells arising principally at the edges of the valves, giving these cells the 
ability to absorb and transmit nutriment from the lymph fluids of the cyst cavity. 
