Physiology. G7 
the young clams were kept suspended in this instance on account of 
their accidental and supplementary adhesion to the Ascidians can- 
not be determined, but it is fair to suppose that their period of sus- 
pension would be prolonged on that account beyond the usual time. 
The presence of a byssal attachment in My a arenaria reopens the 
question of the life-history of this important shell-fish. In fact, it 
is probable that some of its allies may have an unknown byssal 
stage, and, perhaps, types somewhat distant from it in the system, 
but with similar habits in the adult condition, such as Glycimeris 
and Panopma, may also have such a stage. In that case the 
methods hitherto proposed to be adopted in order to secure the 
young for purposes of transplanting would have to bo greatly 
modified. It is very probable that this arrangement is a protective 
one and that the suspension of the young of Mya arenaria is for the 
purpose of protection during the early and most precarious period 
of existence of the animal. To obtain the early stages of the young 
ti will accordingly be necessary to resort to some form of " col- 
lector " or cultch, such as is used in oyster-culture, to allow the fry 
to affix itself. 
While there is a very sharply defined homogeneous larval shell or 
protoconch in the young oyster, this seems to be absent or not 
sharply defined in the young of Mya arenatna in specimens two to 
three millimeters long. In Ghlamydoconclia the protoconch or lar- 
val shell is preserved even in individuals supposed to be adult, since 
here both valves are completely invested by the closed mantle sac, 
the shell being internal. The detection of a byssus in the young of 
Mya is of interest also from the fact that it suggests that "^such or- 
gans are probably present in the voung stages of still other Lamelli- 
branchs, where it has not been hftherto suspected.— Jo/i?i A. Ryder. 
PHYSIOLOGY.^ 
Ox THE Rhythm of the Mammalian Heakt.— Prof. John A. 
McWilliam,2 of the University of Aberdeen, extends to a study of 
the mammalian heart the methods of work which in the hands of 
Gaskell, Mills, himself, and others have led recently to such valuable 
results concerning the organ in Pishes, Amphibians, and Eeptiles. 
nd partly > 
ivhich he co 
' This Department is edited by Dr. Frederic S. Lee, Bryn Mawr Col- 
