G THE VOYAGE OF H.M.S. CHALLENGER. 



of Teihywm and Ascidium under one name, and this was afterwards effected by Linnaeus 

 (Sys. Nat., 12th ed.), who designated the genus Ascidia. 



Bolten's papers on the remarkable form which bears his name were published in 

 1770 and 1771, and the observations of Gaertner, Forskal, Phipps, Pallas, Dicquemare, 

 Fabricius, and others, all of whom described and usually figured new species of Simple 

 Ascidians, appeared during the next ten years. The most important contribution of this 

 period (the end of the eighteenth century) was the work of 0. F. Midler. His Pro- 

 dromus was issued in 1776, and contained a considerable list of named species of Tunicates, 

 while his great work, the Zoologia Danica, gave most valuable descriptions and figures of 

 twenty species. 



Bruguiere, in the Encyclopedic Methodique, collected all that had been done previously, 

 but added little that was new or important. His work, therefore, represents the state of 

 knowledge of the group up to the year 1800. 



In the commencement of the present century valuable anatomical researches were 

 made by Schalk, Carus, and especially Cuvier, who arranged the Ascidians along with the 

 Mollusca under the name of Acephala nuda. At this period also, the genus Pyrosoma 

 was described first by Peron, and afterwards by Peron and Lesueur ; and the latter in 

 conjunction with Desmarest wrote a memoir upon the structure of Botryllus. But by far 

 the most important contributions of this period were the celebrated memoirs of Savigny, 

 pubbshed in 1816.. This author first satisfactorily elucidated the structure of the Com- 

 pound Ascidians, and distinguished them from the Alcyonarians with which they had 

 previously been confounded. His accounts of the different genera which he instituted, are 

 models of patient and careful research, and the accuracy of his descriptions and figures is 

 wonderful. 



Savigny's memoirs upon the Simple Ascidians are no less remarkable. He broke the 

 group up into four great genera — Phallusia, Cynthia, Boltenia, and Clavelina — which 

 might almost be taken as types of the four families, Ascidiicke, Molgulidaa, 1 Cynthiidae, 

 and Clavelmidse. Some of these genera he further divided, and these subdivisions are 

 in several cases now recognised as genera ; and finally he described and figured a large 

 number of new species. Lamarck, in his Histoire Naturelle, profiting by the anatomical 

 discoveries of Cuvier and Savigny, characterised a number of Ascidians, Simple as well as 

 Compound, and arranged them as a class, the Tunicata, intermediate between the Eadiata 

 and the Vermes. 



Every year now brought new additions to our knowledge. Chamisso made his well- 

 known observations upon Salpa about this time, and first noticed the series of phenomena 

 afterwards more fully described by Steenstrup in 1842 as "alternation of generations;" 

 while a little later we have Kuhl and van Hasselt's investigations upon the heart of the 

 same form, resulting in the discovery of the alternation in the directions in which the 

 wave of contraction passes along the heart, and the blood flows in the vessels. 



1 Taking Savigny's Cynthia dione as a Mohjula, which it probably is. 



