1eiKe) TUNICATA CHAP, 
indicated by a line diverging from near the point (3) in the 
phylogenetic diagram below. 
General Conclusions. 
The following diagram is a graphic representation of the 
genetic affinities, or what is now generally supposed to have been 
the probable course of phylogeny of the Tunicata. It will be 
noticed that it shows (1) the Proto-Tunicates arising from Proto- 
Chordata, not far from the ancestors of Amphioxus (see also, this 
vol. p. 112); (2) that the Larvacea are regarded as the most 
Molgulidae 
Ascidiidae 
—-Amphioxus (5) Cynthiidae. 
2 Larvacea -2 
a ‘ g 
= | s (6) Polystyelidae 
= (1) (2) nis Botryllidae 
= Proto-Tunicata. = Distomatidae 
& Ke ® | Didemnidae and 
Doliolidae— | | Diplosomatidae 
[AON ESS Se ives 
Salpidae — 
Eee Pyrosomatidae 
primitive section of the group; (3) that the Thaliacea (Dolio- 
lidae and Salpidae) are supposed to be derived not directly from 
primitive pelagic forms, but through the early fixed Ascidians, 
not far from (4) the ancestral compound Ascidians, which gave 
rise to the Pyrosomatidae; (5) that the Ascidiidae and other 
higher Simple Ascidians are derived, like the Compound Ascidians, 
from ancestral Clavelinidae; and (6), that the Ascidiae Compositae 
are polyphyletic, the Holosomata (Botryllidae and Polystyelidae) 
being derived from ancestral Simple Ascidians independently 
of the Merosomatous families. 
The Tunicata are remarkable for the variety in appearance, 
structure, and life-history which they present. No group illus- 
trates in a more instructive manner so large a number of 
important biological principles and phenomena. They show 
solitary and colonial forms, fixed and free, pelagic and abyssal. 
The development is in some cases larval and with metamorphosis, 
in others abbreviated and direct. Persistent traces of ancestral 
characters are seen in the embryonic and larval stages, while the 
adults present the most varied secondary adaptations to littoral, 
