4940 THE ZooLoGist—JUNE, 1876. 
last Whitsuntide a tank at the Manchester Aquarium, devoted 
especially to tube-worms and containing some remarkably fine and 
luxuriant groups of this particular species collected on the Devon- 
shire coast, exhibited signs of unusual turbidity. The water for 
some distance above the top of the tubes was much clouded, 
and on closer observation it became apparent that these worms 
were themselves the producers of the turbidity. Here and there 
little clouds of granular matter resembling smoke were being shot 
out of the apertures of the tube, the entire effect produced sug- 
gesting the silent discharge of mimic artillery. Sometimes there 
was a lull for a few minutes, when suddenly the bombardment 
commenced again at some outlying station, followed, as though 
directed by electric agency, by a general salvo along the whole 
line. That there are two sexes of the Serpula has been long since 
satisfactorily established, and it was easy, even with the unassisted 
eye, to detect the difference between the male and female elements 
ejected ; the aid of a strong magnifying power, however, still more 
completely confirmed the essential distinctions. After mingling 
with one another, the cloud of milt and ova gradually dispersed 
itself through the water, doubtless proving the origin of the innu- 
merable young individuals that have since made their appearance 
in the tanks. 
A question concerning the habits of the oyster, of very trivial 
importance compared with the manner of its propagation, but at 
the same time almost equally disputed, is that of its position on 
the ground or other fulcrum of support in a state of nature— 
whether, in fact, it rests with the flat or convex shell downwards. 
Almost all authorities, in books and elsewhere, persist that the 
convex valve is the one that takes this position, the flat one being 
the upper and outer one. Such an assumption, however, is entirely 
at variance with what might be logically anticipated, or indeed 
with what is known to occur in parallel instances. Furthermore, 
the oysters themselves afford direct evidence to the contrary. 
Growing upon a flat surface, it is only natural that the upper or 
outer of the two shells should be the more convex one; and that 
such is the case is amply illustrated in the case of the saddle-shells 
(dnomia). Anyone, however, desirous of satisfying himself more 
fully on this point should examine a series of rough Channel 
oysters just brought in from the sea. It will be then observed that 
the delicate hydroid zoophytes, Tubularia, Sertularia, &c., as also 
