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BULLETIN OF THE BUREAU OF FISHERIES. 
The role played by the mantle cells during parasitism and the changes that 
occur during transformation are alike most interesting, and a continuance of these 
studies (which the writer intends to carry out) will probably result in the finding 
of still further adaptations that will make this an attractive and valuable field for 
study. These changes are correlated with embryological development as a whole; 
but since the development of organs of mesodermal or endodermal origin are very 
similar with different mussel species and differ only in the extent of development 
prior to and at the completion of the encystment stage, they are referred to only in 
so far as they have any relation to mantle cell conditions. Whenever citations are 
made in this paper to mussel literature they are so stated, with the author referred 
to; otherwise all statements herein are the result of the worker’s observations. 
MANTLE CELLS OF GLOCHIDIUM. 
In order to understand the references that follow, it is necessary to have a slight 
knowledge of the histology of the glochidium, and this is briefly described from the 
standpoint of the mantle cells, since a more detailed 
treatment is not necessary in a study of this nature. 
The mantle consists of two layers. Immedi- 
ately underlying the internal surface of each valve 
of the shell is a very thin membrane, which repre- 
sents the inner mantle (fig. 1). This lies between 
the valves and the remainder of the glochidial 
tissue, with the exception of the areas of attach- 
ment of the adductor muscle. It is sometimes 
difficult to distinguish in the glochidium, but less 
so during later development, when the cells in- 
crease in size and become somewhat conspicuous. 
Covering this layer, in turn, are the large cells 
giving rise to the outer mantle, which overlies the 
greater portion of the interior of the glochidium. 
This mantle is in the form of two folds — one for 
each valve — which are continuous with each other 
with the exception of a small area ventral to what 
Lefevre and Curtis have termed "the area of 
flexure.” On each lateral portion of the mantle 
these cells are large, flat, and deeply granulated, with large nuclei (fig. 1). Ventral 
to the adductor muscle, however, the mantle cells are extremely flat, with smaller 
nuclei, and the granulations are absent (fig. 1) . 
On the posterior side of the adductor muscle is a group of crowded cells with 
large nuclei. Lateral extensions of this tissue, which is of mesodermal origin, give 
rise to the heart, pericardium, and kidney, and extensions backward, somewhat 
under the mantle (fig. 2, l. p.), represent lateral pits from which the gills originate. 
These lateral pits enter largely into the mantle cell transformation of the Anodontas. 
Of the median group of cells the upper or ectoderm cells give rise to the covering 
of the foot fold; the deeper cells are the endoderm. This area is the only portion 
Fig. 1— Section through adductor muscle of 
glochidium of luteola. s.c., sensory cells; l. m. c., 
large mantle cells; in. m., inner mantle; ad., 
adductor muscle; z. g 
