STRETHILL WRIGHT, ON BRITISH ZOOPHYTES. A7 
invisible to the naked eye—that we must wait for further 
development before we can determine their identity. Ge- 
genbaur has proved that the Medusoid of Velella acquires a 
further number of canals and tentacles; and I have elsewhere 
recorded the successive changes which oceur in the Medusoids 
of several species of Atractylis. It is also certain that such 
increase in the number of elements (canals, lips, tentacles, 
and otoliths) does occur in quorea vitrina, for the smaller 
specimens have always a less number than the larger. Mean- 
time the question as to the larval state of quorea vitrina is 
settled. This, the largest of all the naked-eyed Medusas, is 
the reproductive phase of one of the smallest of all the Hy- 
droide. 
2. Reproduction of Atractylis arenosa, Alder. (Pl. TV). Com- 
municated to the Royal Physical Society of Edinburgh, 
February 26th, 1862. 
This zoophyte was described by Mr. Alder at the last meet- 
ing of this society. In September last I found a large female 
specimen at Largo, and was fortunate enough to have an op- 
portunity of studying its anatomy and reproduction. The 
polyp-stems are, as Mr. Alder has shown, funnel-shaped and 
expanding at the top. From them the milk-white polyps 
issue, each furnished with an alternating row of long tenta- 
cles. The scleroderm, or corallum, is covered by a thick layer 
of colletoderm, which is continued over the body of the polyp, 
and which, when the polyp retires within its tube, fills up the 
- top of the tube by its cushiony folds, so that the polyp is 
completely hidden, and the funnel appears, as it were, closed 
by a valve. The colletoderm in my specimen was coated and 
impregnated with mud. Mr. Alder’s specimen was covered 
with grains of fine sand. I was at first inclined to believe 
that this zoophyte was merely a variety of Atractylis repens, 
which, with its Medusoids, I have already described to the 
society; but after it had been in captivity a few days, I found 
that it was beginning to put forth ovisacs, one on opposite 
sides of the polyp-stems (Pl. IV, fig. 7). 
The mode of reproduction in this zoophyte is unique 
amongst the Tubulariade, though I have noticed and de- 
scribed it in the Sertularias and Campanularias. 
The female generative sac of Atractylis arenosa resembles 
that of Hydractinia; it is a simple sac, formed of ectoderm, 
or the outer layer of the ccenosare, enclosing a similar sac of 
endoderm, the “placenta,” the whole being covered by a 
layer of scleroderm and colletoderm. Between the placenta 
and the ectoderm a large number of ova are developed, each 
