310 
Z. ASC1DIOIDA. 
Cristatella, 
to the naturalist a spectacle of such singular curiosity and beauty 
as perhaps can meet its superior or rival in no other creature. I f 
am unwilling to borrow, from the memoirs of the foreign authors, 
any additions to Sir J. G. Dalyell’s short history, for I am aware of 
the confusion to which such a practice has occasionally led, but no 
harm can arise from the mention of some particulars which are evi- 
dently generical. I may state then, that the tentacula are ciliat- 
ed like those of other ascidians ; the intestine has an oral and anal 
aperture, the latter with a medial position ; and there is no trace of 
any organ like what, in some other families of the order, has been 
reckoned an ovary. The egg, according to M. Turpin, forms a small 
flattened sphere with a papillous surface slightly incrusted with cal- 
careous matter. The centre is of a dark reddish-brown or vinous 
colour, the margin more transparent and yellowish, proving that the 
egg is, vesicular,— the exterior circle marking out the thickness of 
the cocoon or shell, and the more opake disk the part occupied with 
the embryotic fluid. About 16 rough spines radiate stiffly from 
the circumference : they are tubular, yellow, terminated with from 
two to four crotchets, and apparently vary in length, for they arise 
alternately from the edge and from the surface a little behind this.* 
The egg is filled with an albuminous granular fluid analogous to the 
vitellus or yolk, for in it the foetus is perfected after a period which 
probably depends, in a great measure, on the temperature of the sea- 
son in which they are laid. The time of birth having arrived, the 
shell opens in two gaping halves, as an oyster opens its valves, to 
permit the escape of the young polypus, which enters on its existence 
complete in all respects, either a single individual, or with one or 
two others, less mature, pullulating from the sides. 
One of the most interesting facts ascertained by M. Turpin is 
that the eggs before exclusion, and immediately after, are oval or 
lenticular, and entirely free of the spines which roughen them at a 
later stage. Hence an easy solution of a question touching the man- 
ner of escape from the mother, which, before this discovery, seemed 
incapable of being effected without a painful laceration from their 
bristling armature. This alteration in the structure of the egg is 
very remarkable, although not singular, for the eggs of several mites 
* According to M. P. Gervais this is not the case,— the spines orignate sole- 
ly from the line of junction between the marginal band and the disc ; — “ du point 
de contact de cet anneau et du corps disciforme partaient sur Tune des faces les 
crochets dont j’ai parle. Je reconnus depuis que 1 ’autre face presentait aussi 
les appendices en crochets, mais qu’ils y etaient moins allonges.” 
