392 ZOOLOGY 
metrical relation of parts seen in the true worms, and which 
strongly suggest the conclusion that the Tunicates are mod- 
ified worms. This conclusion is strengthened. by the fact 
that in Appendicularia the ventral nervous cord is ganglir 
onated at intervals, as in the Annelids, while the twisted 
digestive tract is much as seen in Polyzoa and Brachiopods. 
Furthermore, the branchial sac is strongly analogous to the 
pharyngeal or gill-sac of Balanoglossus, and this structure in 
the Ascidian and whale’s-tongue worm anticipates the pha- 
ryngeal or gill-sac of Amphioxus and vertebrate embryos. 
The simple Ascidians attain to a large size, Ascidia callosa 
being about ten centimetres in diameter, quite round, and in 
form and color bears a strong resemblance to a potato. 
Ascidia gigas, dredged by the Challenger Expedition, is from. 
thirty to forty centimetres in diameter, and has a ganglion 
nearly as large as a pea. A floating colony of Pyrosoma 
gigas is sometimes five feet long. Cynthia pyriformis Rathke 
may be called the sea-peach, from its size, form, and the rich 
bloom and reddish tints of its test. It is common in deep 
water from Cape Cod to Greenland and Scandinavia. 
While the Ascidians as a rule do not live below a depth of 
150 fathoms, the stalked Hypobythius calycodes Moseley was 
‘dredged by the Challenger Expedition in 2900 fathoms in 
the North Pacific Ocean; it is stalked, and about twenty 
inches high. The aberrant Octacnemus bythius Moseley was 
also dredged in 1070 fathoms near the Schouten Islands, 
Tasmania. 
Panceri has described the luminous organs of Pyrosoma, 
which is highly phosphorescent ; the substance from which 
the light is emitted is probably a fatty matter. : 
Ascidians multiply by budding and by eggs. Examples of 
budding or germination are seen in the compound or social 
Ascidians, such as Amarecium, etc., where the individuals of 
the colony byd out from the primitive one just as it has left 
the larval condition and has become fixed. In Didemnium 
buds arise from masses of cells floating free within the test. 
They multiply by division as soon as the digestive and repro- 
ductive organs are indicated. In Botryllus the zooid which 
results from the tadpole-like larva serves, according to 
