THE PYROSOMA. 325 
Few bodies among the forms of animal life exhibit such exquisite 
figures as those which we see displayed in the combinations of 
these compound Ascidians.” 
In the genus Diazona, which has its chief seat in the Mediter- 
ranean, the animals, which are very prominent and arranged in 
concentric circles, form a single system expanded into a disc like 
that of a flower or of an Actinia. The anal orifices, it will be 
seen, are situated close to the branchial apertures at the free end 
of the single animals, while in the Botrylli 
they open into a central excretory cavity. 
In the Pyrosomes we find large co- 
lonies of small individuals aggregated in 
the form of a cylinder open at one end. 
Their mouths or anterior extremities are 
situated on the exterior of this hollow 
body, which they bristle with large and 
longish tubercles (a), whilst the opposite 
or anal orifices (b) open into the cavity 
of the cylinder, whose smooth wall they 
perforate with numerous small holes. By 
a simultaneous action the central cavity is 
either narrowed or enlarged, and by this 
means the strange social republic glides 
slowly through the waters. 
The Pyrosomes inhabit the Mediterra- 
nean and the warmer parts of the ocean. 
In the former at times their abundance is 
a source of great annoyance to the fisher- 
men, sometimes even completely clogging 
their nets, and on the high seas they are 
not seldom met with in almost incredible 
profusion. Their delicate and transpa- , so Ve SR aA aS, 
Sg j . ints ip Pyrosoma giganteum, cut 
rent forms, their elegant tints, and their Py eee Sl eae eum cut 
unrivalled phosphorescence render them PEC epee 
: ° . a. Branckial or external ori- 
objects of admiration to the voyager, and fice. 
, &. Anal or internal orifice. 
entitle them to rank amongst the most @. Stomach. e. Liver. 
ae Jf. Branchie. 
resplendent living gems of the ocean. 
While the sessile Ascidiz remind one of the polyps, the 
transparent Salpz, freely swimming in the sea, bear a great 
resemblance to the pellucid jelly-fishes. Each resembles a 
Z 
