SIGNIFICANCE OF LARVAL MANTLE OF FRESH-WATER MUSSELS. 
207 
tion to a nutritional character, have become greatly enlarged, the micronuclei also 
becoming large and distinct. Faussek speaks of these ingested cell elements while 
being consumed lying in special vacuoles, which at times take up the greater part 
of the cells, these vacuoles being similar to the food vacuoles of Protozoa. Although 
such a condition undoubtedly occurs, it is probably not as conspicuous as Faussek’s 
words might infer, and the writer has not been able to determine this condition 
as at all prominent. Vacuoles have been seen inclosing food matter, but in other 
cases they were observed having no connection with ingested material, and 
they may represent merely a vacuolated condition not necessarily of a digestive 
nature. 
It was found with Anodonta corpulenta that the disintegration of the inclosed 
tissue progressed slowly for at least two days at a temperature of 18 ° C. before the 
epithelial cells of the host tissue were completely 
utilized, and it required at least another day 
before the ingested cell matter in the mantle 
cells disappeared. During all this period the 
mantle . cells became larger and the vacuolated 
condition more pronounced, so that it is hard to 
escape the conclusion that there is an actual 
increase in size as a result of the ingestion of 
the not inconsiderable amount of food, and this 
is supported by the fact that during this short 
period of three days the development of the 
larva progressed very slowly, the lateral pits 
became more pronounced, and the endoderm 
sac conspicuous; yet there was no growth of the 
remaining organs commensurate with the large 
amount of food ingested. 
In the glochidium the cell boundaries of the 
larval mantle are indistinct, and as parasitism 
progresses a fusion of the cells takes place, so 
that the mantle at the end of the first three 
days appears only as an enlarged, clear, vacuo- 
lated mass, with the outer edge or surface very 
irregular, characterized by the large nuclei with 
conspicuous nucleoli, so different from the nuclear structures of the remainder of 
the organs of the developing larva. 
Up to this time the mussel has passed through what might be termed the first 
encystment stage. With the examples of corpulenta that have been studied this 
covered the first three days of parasitism. During this period the mantle under- 
went a remarkable histological metamorphosis, and nutrition by reason of these 
mantle cells occurred in an intracellular manner. This method of intracellular 
nourishment, as Faussek points out, is present with the embryos of mammals. 
The cells of the chorion villi and the chorion epithelium, especially, possess this 
phagocytic ability. With the ruminants they take in the elements of the uterine 
Fig. 3— Section through encysted glochidium 
of A. corpulenta, one day after attachment, 
showing fusion of mantle cells, with pseudo- 
podial processes noticeable. Ingested food 
material visible, n., nucleus of larval mantle; 
in. nuclei of ingested cellular detritus. 
