Tank No. 20. 
65 
carried by currents to the coasts, where they 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 No. 20) where the structure of the larger forms, such as Salpa 
maxima-afrieana (Fig. 113) may be readily followed. The outer wall 
of the barrel-shaped body is like the tunic of the Ascidians, and presents 
a pore 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 
Fig. 113. Single individual of Salpa maxima-afrieana , nat. size. 
swimming-cavity. The animals swim with their anterior extremity (the 
right-hand side in Fig. 113) in front, taking in the water by the 
Fig. 114. Chain of Salpa maxima-afrieana, Salpa pinnata, 
Y 2 nat. size. 1 , / 2 nat. size. 
anterior pore, or mouth, into the 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 contraction 
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. 113) a brown globular mass, the 
stomach and intestine, will be noticed. In front of it lies the trans¬ 
parent heart, which in all Tunicata contracts for a few minutes from front 
to back and then from back to front, so that the circulation of the blood 
is periodically changed. 
The development of the Salpae is of great interest. The poet Cha- 
misso, who was also a very good zoologist, was the first to observe 
on his voyage round the world, that in Salpa the offspring does not 
