Tunicata. j o I 



very often find their way into the nets of the fishermen, much 

 against the wish of the latter. In the Aquarium they will be almost 

 always seen in spring and autumn (tank Nr. 20) where the structure 

 of the larger kinds, such as Salpa maxima-africana (fig. 95), may 

 be readily followed. The outer wall of the barrel-shaped body 

 is like the tunic of the Ascidians, and presents a hole at each 

 end. The throat is in Salpa, however, literally nothing but gill- 

 slits, its wall being represented only by a slanting bar (observe 

 vibrating hairs) leading from the mouth to the stomach across 

 the great swimming-cavity. When this is filled with water, the 

 mouth is closed, and the muscular bands, which surround the 

 body like hoops of a barrel, are forcibly contracted. This con- 

 traction forces the water out through the hinder or outgoing 

 pore and the animal is jerked forwards. It thus sucks its way 

 through the water. At the hinder end of the body (left in fig. 96) 

 a brown globular mass, the stomach and intestine, will be noticed. 

 In front of it lies the transparent heart, in which the reversal of 

 the blood-stream mentioned above can be very well observed. 

 The development of the Salpce is of great interest. The poet 

 Chamisso, who was also a very good zoologist, was the first to 

 observe on his voyage round the world, that in Salpa the off- 

 spring does not resemble the parent form, but the grand-parent. 

 Thus in one species we have two forms which alternate with each 

 other (cf . p. 69) ; one form he found always as a single individual, 

 whereas the other one occured in chains consisting of a large 

 number of individuals. Later observations have entirely confirmed 

 the accounts of this "Alternation of generations" of the Salpce. 

 In the Aquarium visitors will find both chains (fig. 93 and 94) 

 and single individuals (fig. 105) of the same species; the chains 

 are sometimes of considerable length, or they may form a closed 

 ring (fig. 94). The members of such a chain are exactly alike, 

 and are hermaphrodite. Their eggs never hatch into chains, but 

 always into single individuals, which are not only different anatom- 

 ically from their parent but also never produce eggs. Instead 

 of this they give rise to buds, which are small chains of SalpcB 

 and are liberated after attaining a certain size. Like Pyrosoma 

 the SaipcB are phosphorescent animals. 



In connection with the Tunicata we may mention the Lancelets, 

 which are looked upon as the lowest vertebrate animals. The 

 Neapolitan Lancelet, Amphioxus lanceolatus (fig. 65) is scarcely 

 2 inches long, colourless and translucent; its only skeleton is a 

 notochord; it has no head. Instead of a heart it has pulsating 

 vessels containing colourless blood, and like the Tunicates it has 



