THE 
VOYAGE OF H.M.S. CHALLENGER. 
ZOOLOGY. 
REPORT on the Tunicata collected during the Voyage of H.M.S. 
Challenger during the Years 1873-76. By William A. Herdman, 
D.Sc., F.L.S., F.R.S.E., Professor of Natural History in University 
College, Liverpool. 
PART II.— ASCIDI^ COMPOSITE. 
PREFACE. 
The first part of this Report, treating of the Ascidia: Simplices of the collection, was 
published in the end of 1882, and at that time it seemed probable that the remainder 
of the Tunicata could be described in a second and considerably smaller part which 
would be ready for publication some time in 1884. The Compound Ascidians, however, 
proved on careful examination to be a much larger and more varied group than had been 
anticipated. On account of the difficulty in finding good diagnostic characters, and of 
the similarity which different species sometimes show in their external appearance, it has 
been necessary to submit nearly all the specimens in the collection to a detailed histo- 
logical examination, and portions of most of them have had to be sectionised — a slow 
and laborious proceeding — before the relations of their different parts could be satis- 
factorily determined. Then, in the case of a few species, some interesting peculiarities 
in regard to reproduction by gemmation, having an important bearing upon the mode 
of formation of the colony, required a careful and lengthened examination. For these 
(ZOOL. CHALL. EXP. — PART XXXVUL — 1886.) Fp 1 
