1886.) Zoology. 1059 
in the aquiferous system of Ophiactis (Bull. Acad. Roy. Belgique, 
1, xlix, p. 402, 1880) appear to have escaped Dr. Horrell’s notice. 
THE ByssAL ORGAN IN LEMELLIBRANCHS.’—The first portion of 
Dr. Barrois’ article is a very full description of the byssal organs 
or its remains in forms from almost every family, twenty-one in 
all, and in forty-nine species of lamellibranchs. There is also 
a historical résumé of the subject, description of additional glands, 
and a discussion of the homologous organs in gasteropods. 
In Cardium edule the organ is described in full and others are 
compared with it. Its parts are: 1. “The cavity of the byssus,” 
a large space in the center of the keel of the hatchet-shaped 
foot. 2. “The canal of the byssus,” opening on the surface by a 
. 3. “The byssus,” a hyaline thread running out from the 
cavity through the canal. 4. “ Byssal glands,” glandular cells 
lying below the epithelium and opening separately into the 
cavity. 5. “The groove” running forward from the canal along 
the margin of the foot to the anterior end. 6. “Glandular cells 
of the groove” opening into it among the epithelium cells. The 
epithelium is everywhere perfectly continuous and in the cavity 
is thrown into numerous lamellar folds. 
Various departures from the plan are described and figured; 
there may be no functional byssus but the other parts may all 
be present, or the groove, or the glands, or even the cavity may 
be wanting, or there may be in the adult no trace of any of the 
organs. In the same family or even genus wide variations may 
occur. Thus Tapes virginea has no functional byssus, the cavity, 
glands and lamellæ are present, while in Venus rudis and other 
lateral attachment of the creature. The “cornet” of Anomia, 
with its groove leading to the byssal cavity, is similar to the 
muciparous gland on the anterior part of the foot of Pecten maxi- | 
mus. In Unio and Anodontaa cavity in the keel of the foot is the 
only remains of the byssal organ in the adult. This, doubtless 
the water pore of Kollmann, Griesback and others, is lined 
with continuous epithelium. It is to be regretted that lack of 
material has prev@nted research into the embryonic condition of 
many of the retrograde forms. 
Barrois also describes as characteristic of the lamellibranchs 
special muciparous glands in the anterior portion of the foot s 
these in some cases line the inside of a cavity, e. g., Pecten 
maximus, in other cases the organ being everted they line the 
, Lille, 1885, pp. 160, pl. x. 
1 Les Glandes du Pied et les Pores Aquiferes chez les Lamellibranches—Par le Dr. . 
Ih. Bartol i | : 
