INTRODUCTION. 



I SHALL follow here the same plan which I adopted in the preceding part of this 

 Eeport, and give, along with a supplementary bibliography, a short account of the 

 history of the groups to be described farther on, 



HISTORY. 



The group Tunicata when first established as a class by Lamarck' in 1816, contained 

 only two pelagic forms, Salpa and Pyrosoma. Of these the genus Saljya had been 

 established by Forskahl in 1775, but some of the forms which are now referred to it or 

 to Cyclosalpa had been previously described more or less fully under the names 

 Holothuria (Linnaeus), Holothurium (Pallas), TJialia (Browne), and Dagysa (Banks). 

 Forskahl had been fortunate in finding a large proportion of the existing species of 

 Saljja, and much of the confusion in the group has been caused by other authors since 

 re-describing his species under new names, generic and specific. 



Pyrosoma had been first made known by Pdron in 1804, and was shortly afterwards 

 treated more fully by Lesueur and Savigny. These researches, along with those of 

 Cuvier on the anatomy of Salpa, showed the relationship of those pelagic forms to the 

 Simple and Compound Ascidians then being investigated by Savigny, and enabled 

 Lamarck to unite them all in the class Tunicata. 



A few years afterwards, in 1819, Chamisso published the observations made during 

 his celebrated voyage round the world, and announced the imjjortant discovery that 

 Salpa in its life-history passes through the series of changes which were afterwards more 

 fully described by Steenstrup in 1842 as alternation of generations. He observed first 

 that each species of Salpa had two forms which were produced alternately, so that, as 

 Chamisso put it, "a Saljja mother is not like its daughter or its own mother, but 

 resembles its sister, its grand-daughter, and its grand-mother." 



The next discovery of importance was likewise made on Salpa. In 1822, Kuhl and 

 van Hasselt observed the alternation in the direction in which the wave of contraction 

 passes along the heart, and in which the blood circulates through the body. It has 

 since been found by many investigators that this remarkable observation, first discovered 

 in the case of Salpa, holds good for all groups of the Tunicata, 



1 For references to the literature, see Part L, Bibliography ; and also farther on in the present part, under the 

 various faniihes and genera. 



