644 DAVID HILT TENNENT. 
Haswell (23) describes and figures a Bucephalus from 
sporocysts in which the germinal epithelium contained a red 
colouring matter. In other respects there seems to be little 
difference between this and B. haimeanus, 
Observations on B. haimeanus, Lacaze Duthiers = 
B. cuculus, McCrady. 
The form upon which my observations have been made is 
presumably that described by McCrady (21) as B. cuculus. 
McCrady’s account is not fully satisfactory as it seems to have 
been written some time after the observations were made and 
then from insufficient notes. 
In the examination of a large number of oysters one finds 
them in many stages of infection. For convenience of de- 
scription we may consider them under four stages. 
1. Individuals in which infection is recent. Examination 
with a lens magnifying about ten diameters or more, or 
examinations with the naked eye reveals little irregular 
patches, somewhat whiter in colour than the surrounding 
tissue, lying just beneath the outer covering of the reproduc- 
tive glands. Upon tearing the oyster tissue with needles 
similar patches may be found within the substance of the 
gonad. ‘These patches are comparatively young sporocysts. 
They consist of a central bladder-like body from which short 
branches are given off (figs. 2 and 3). 
They may readily be separated from the surrounding tissue, 
and examination with a higher magnification will show that 
there are opaque masses of cells, the germ-balls, within the 
cavity of the central body. 
i. In more advanced stages of infection the branches of 
the sporocyst have grown in length perceptibly and have be- 
come “germ-tubes” (fig. 4), which occupy intercellular spaces 
within the host (fig. 14). The number of germ-balls has in- 
creased greatly and various stages of development are seen, 
some of the germ-balls having given rise to well-developed 
cercarie. 
