Vou. 2} Ritter—The Pelagic Tunicata. 97 
(ec) Phorozooid.—Entirely similar to gonozooid except for 
absence of gonads and presence of ventral process which is rela- 
tively long and eylindrieal. 
(d) Trophozooid—Small, but long in proportion to breadth, 
and with a relatively long peduncle. 
As already said, D. miilleri is the least abundant of our spe-’ 
cies. Thus far it has been taken in mid-summer only, off San 
Diego. 
Order I1.—ASCIDIACEA de Blainville, 1827. 
Pelagic or sedentary urochorda, with proportionally very 
large branchial sac having many stigmata. Branchial and atrial 
openings not at opposite ends of body, except in Pyrosoma. 
Test in most cases large in quantity and forming a common 
matrix in which the zooids are embedded in most colonial forms. 
A free swimming larval or ‘‘tadpole’’ stage in the life career of 
nearly all species, this undergoing a profound metamorphosis 
to give rise to the adult. An asexual reproduction by budding 
in many, but no true alteration of generations or polymorphism, 
as in the Thaliacea. 
Fam. PyrosoMIDAE T. Rupert Jones, 1848. 
Pelagic colonial Ascidiacea, with the colony in the form of a 
hollow eylinder closed at one end. Zooids embedded in the thick 
test constituting the greater part of the wall of the cylinder, and 
so arranged that the branchial orifice opens on the external sur- 
face of the cylinder, while the atrial orifice opens into its inte- 
rior; branchial and atrial orifices consequently at opposite ends 
of the zooid. Branchial sac very large, the stigmata placed per- 
pendicularly to the endostyle, each extending from the endostyle 
to near the mid-dorsal line. No peribranchial chamber present, 
the atrial orifices opening directly into the great common cloaca, 
which constitutes the hollow of the eylinder of the colony, as 
above indicated. Embryo arising from the egg, known as the 
‘‘eyathozooid,’’ giving origin, by a peculiar process of trans- 
verse fission, to the first four blastozooids, from which as the 
starting point the remainder of the colony arises by typical ascid- 
ian budding. Species all, so far as known, highly phosphorescent. 
