322 THE INHABITANTS OF THE SEA. 
the antechamber of the alimentary canal, which is barely 
distinguishable into gullet, stomach, and intestine, and always 
convoluted or folded once on itself. The Tunicata are ex- 
clusively marine, and widely spread from the arctic to the 
tropical seas. All of them are free during the earlier parts of 
their existence; some remain permanently so (Pyrosomide, 
en 
ceca 
MS 
Clavellina producta. Group of two adult Ascidia mammillata. 
and several young individuals, mag- a. Branchial orifice, open. 
nified about five times. b. Anal orifice, closed. 
c. Branchial orifice. e. Branchiz. #. Anal orifice. 
Z. Stomach. o. Heart. wu, wu’, u’’. Reproductive 
buds, springing from the abdomen of the adults. 
Salpze), but the generality (Ascidiz, Botrylli) become fixed to 
shells and other marine bodies; some exist as distinct individuals 
(Ascidiz, Cynthia), whilst various degrees of combination are 
effected by others (Botryllus, Clavellina, Pyrosoma), and some 
are simple in one generation and combined in the next (Salpe). 
