LIFE-HISTORY OF BUCEPHALUS HAIMEANUS. 645 
ut. In still more advanced stages nearly the whole sub- 
stance of the oyster has been replaced by a mass of white 
fibres—the germ-tubes. At this stage the oyster may still 
appear plump and healthy, a rather chalky whiteness being 
the only difference in appearance between an infected and a 
“fat”? uninfected oyster. So tightly is the visceral mass 
packed with the branching germ-tubes that a slight cut in 
its surface results in the bursting out of a considerable mass 
of tubes. Upon dissecting the oyster with needles it is seen 
that the germ-tubes not only penetrate the gonads but fairly 
riddle the liver and stretch out into the gills, the palps, and 
even into the walls of the pericardium. 
The germ-tubes at this stage contain embryos in stages of 
development from a single cell to cercariz which are about 
to be set free. 
iv. In the last stages the tissues of the oysters seem almost 
completely wasted away. No trace of the gonads is to be 
seen, while the liver persists as a rounded mass about the 
size of a pea. Upon tearing the outer covering of the body 
germ-tubes may be drawn out; they have lost their whitish 
appearance, have become transparent, seeming, as one draws 
them out, much like viscid strands. Within their lumens are 
found only a few partially-developed cercariz or germ-halls. 
I have examined oysters during every month of the year, 
and on every occasion have found infected specimens. The 
growth of the parasite seems, however, to be most rapid in 
June. My observations lead me to believe that infection 
takes place during the summer months, from June to October. 
At the time that McCrady made his observations he was 
unaware of those of von Baer and Lacaze-Duthiers. Upon 
gaining access to these later he was unable to correlate the 
form which he found with either of the then known varieties. 
Though he did not see anything which might have been taken 
for a mouth, he admits that there may have been one. 
Because of the rigidity of the tubes which, as has been 
already noted, he described, the lack of the striation which 
Lacaze-Duthiers observed and some minor differences, he 
voL. 49, PART 4.—NEW SERIES. 47 
