DEVELOPMENT—GEOGRAPHICAL DISTRIBUTION. Tun. 5 
heart of the Tunicata is an organ peculiar to that group, and is not homo¬ 
logous with the heart of the Vertebrata. They consider all the various 
theories as to the phylogenetic origin of the Tunicata in the light of their 
own valuable contributions to the embryology and morphology of the 
group, and arrive at the conclusion that the Urochorda , the Ceplialochorda , 
and the Vertebrata are to be regarded as derived from three independent 
lines, which arose at the same point from the Protochordata. 
The process of gemmation in Salpa, from the formation of the stolon 
to the completely developed “chain,” is given in detail by SeeligePy (24). 
Barrois (1) gives a detailed account of the process of gemmation in 
Anchinia. The stolon, unlike that of other Thaliacea , is formed by a 
solid cord of endoderm, covered by a layer of ectoderm. Each bud is 
formed as an outgrowth consisting of an ectodermal covering, inside 
which is an endodermal mass composed of different kinds of cells, which 
soon separate into a central portion, the endoderm proper, surrounded by 
a group of nerve cells, a group of reproductive cells, and some scattered 
cells. The endoderm becomes partially divided into two masses, placed 
ventrally—the pharyngeal and the intestinal. It is placed in communica¬ 
tion with the exterior by the buccal and the anal apertures. The nerve 
cells are placed dorsally, and form a tube with terminal enlargements, from 
the anterior of which the subneural gland is formed. The atrium is 
formed as two short tubes, derived from the ectoderm, which place the 
pharyngeal cavity in communication with the exterior. The reproduc¬ 
tive cells are placed posteriorly in the bud. In the sterile zooids they 
remain undeveloped. 
Phylogeny. 
Seeliger (24) discusses the phylogeny of the Tunicata. He considers 
that the ancestral stem, after the separation of the Appendiculariidce , gave 
rise to two divergent branches—one leading to the Simple, Social, and 
Compound Ascidians, and the other to the Pyrosomatidce , Salpidce, and 
Doliolidce. 
[See alsoyunder Development, and under Thaliacea.] 
Geographical Distribution. 
Sluiter (25) describes 16 species of Simple Ascidians, 12 of them new 
to science, and one new variety, from the Island of Billiton, in the Malay 
Archipelago. 
The Simple Ascidians of the coast of Provence are fully treated by 
Roule (20 & 21). He has found representatives of the families Ascidiidce, 
Cynthiidce, and Molgulidce, belonging to 13 genera or subgenera, and com¬ 
prising altogether 28 species, some of which are new. He discusses their 
distribution according to the depth, the nature of the bottom, and the 
condition of the water, and also shows their occurrence, so far as is known, 
in other seas. 
Yon Drasche (7) records 4 species, 3 of them new, of Molgulidce , from 
the Adriatic. 
