6 
THE VOYAGE OF H.M.S. CHALLENGEE. 
discoveries made by Savigny and Cuvier, instituted the class Tunica ta, which he placed 
between the Eadiata and the Yerines in his system of classification. 
In 1826 H. Milne-Ed wards, while investigating along with Audouinthe zoology of the 
Chausey Archipelago, off the coast of Normandy, made a number of observations upon 
Compound Ascidians in a living condition, and laid the foundations for his great work 
upon the group which was published some sixteen years later. He also at the same 
time was fortunate enough to discover the tailed larva, ^ and he traced its development 
into the adult Ascidian. Lister’s observations, published in 1834, were made partly upon 
a species of the remarkable genus Di'plosoma? They referred mainly to the circulation 
of the blood. About this time Forbes and Goodsir, W. Thompson, Delle Chiaje, and 
others were steadily adding to the knowledge of the Compound Ascidians, and in 1842 
Milne-Edwards’ important memoir, “ Observations sur les Ascidies Composees des c6tes de 
la Manche,” appeared, with its fresh anatomical and embryological discoveries, and its 
natural system of classification into (1) Botrylliens, (2) Didemniens, and (3) Polycliniens. 
klilne-Edwards had a great advantage over Savigny and others of his predecessors in 
having worked upon living material ; some of the Compound Ascidians are greatly 
altered by preservation in alcohol. 
Additions to the list of known species were made during the next few years by 
Forbes, Alder, and several others, and the article Tunicata in Todd’s Cyclopgedia, 
published in 1848, gives a good account of the knowledge of the Compound Ascidians 
at that time. A still more complete account was published some years later (1862) in 
Bronn’s Thierreich. Dr. J. Denis Macdonald’s observations upon some of the most 
remarkable forms of the Ascidiae Compositse were made about this time, viz., on 
Chondrostachys in 1858 and on Diplosoma in 1859. These excellent researches will 
be referred to later on in this work. 
In 1862 Gegenbaur gave in Muller’s Archiv an important account of the anatomy 
and development of Didemnum gelatinosum, and, a few years later, Kowalevsky’s great 
memoir on the development of a Simple Ascidian made its appearance and threw 
a fiood of light upon the interesting and peculiar tailed larva which had been described 
but not thoroughly investigated nor understood by Milne-Edwards and others. The 
relationship with the Vertebrata, which Kowalevsky established for the S im ple Ascidians, 
held good of course for all groups of the Tunicata, and the similarity of the main points 
in structure and development between the larva of the Compound and of the Simple 
Ascidians has since been demonstrated by many observers. 
The important observations of Krohn and Metschnikoff upon the process of gemmation 
in the Botryllidaj were published a few years later, and Kowalevsky’s contributions to 
* Tliis, however, liad been figured long before l;y Savigny both for Simple and Compound Ascidians (see M4moires, 
pi. xi. fig 2'^, Clavdina borealis; and pi. xxi. fig. 1, t, Botryllus polycyclus). 
^ Usually referred to as a Leptoclinum. 
