GENUS HYALINIA. Lar 
The Phylacoblasts, within which the Phylacites are developed, were 
formerly mistaken for mucus glands; at first they resemble connective 
tissue, but the protoplasmic contents and nucleus disappear when the 
contained Phylacite is developed. ‘They are restricted to an area, irregular 
in shape and variable in extent, at the most posterior part of the dorsum, 
which is partially overspread by the mantle, and distinguished from the 
surrounding integument by its slighter pigmentation. In adults there is 
but a single layer of Phylacoblasts, whereas in the young there may be two 
or three layers in different stages of development. . 
~ 
BiGs 2% Fic. 28. Fic. 29. Fic. 30. 
Phylacoblast and Phylacites, showing the origin and development of the Phylacite, 
highly magnified (after André). 
Fic. 27.—Phylacoblast, showing a developed Phylacite (f4.), a developing one (A), and the nucleus 
of the secretory cell (72). 
Fic, 28.—Phylacite during expulsion, showing the development of the fungiform shape, and the 
change in position and character of the contained spha:rules. 
Fic. 29.—Phylacite, showing the mushroom form and concentric structure. 
Fic. 30.—Phylacite, with less expanded head, but showing the pointed and now externally projecting 
toxic sphzrules, which during development and before expulsion were rounded and internal. 
A Phylacite (pvAa€, defender) is an ovoid body, about one-tenth of 
a millimetre long, composed of a clear or slightly-yellowish granular sub- 
stance, surrounding a vesicle, containing 3-20 rounded, refractive sphzerules, 
the whole lodged within the parent-cell. On expulsion the Phylacite 
assumes the form of a mushroom, and the internal refractive sphzerules 
become pyriform and protrude beyond the base of the stem, and it has 
been conjectured by Prof. André, their discoverer, that these projecting 
and pointed spherules may be the active defensive agents and possess 
some toxic property. 
Enemies.—Birds are great enemies of the present group, and devour 
at times large quantities. //yaliniw have been found in the crops of 
partially-fledged sparrows, while as many as 416, in addition to other 
objects, have been taken from the crop of a single nestling Stockdove by 
Mr. C. E. Wright. Perhaps, however, the most destructive creatures to 
this and allied groups are the Diptera, which destroy large quantities of 
mollusca even in the egg state. 
Geological History. — According to Sandberger and others, the 
Hyalinie have been found in every formation, from Holocene down to the 
lowermost Eocene, and the first-named author records the genus doubt- 
fully from the ‘‘Steinkohle beds” beneath the lias. In this country, how- 
ever, the genus is not represented from beneath the Oligocene beds, while 
existent species have not hitherto been found below the Pliocene deposits. 
Geographical Distribution.—The genus Hyalinia has a fairly com- 
pact distribution, although extending throughout the Holarctic regions, 
with representative species in more distant regions. It is one of the 
more dominant genera of the present day, and has been spread by com- 
merce to New Zealand, Australia, and other of the weaker zoological 
regions, to the prejudice of their native fauna. 
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