TUNICATES AND ASCIDIANS 475 
Genus Salpa 
The animals of this genus are transparent, subcylindrical, 
smooth, gelatinous bodies encircled by bands of white muscular 
fiber. They strikingly exemplify alternation of generations. 
They occur in two distinct conditions, one being solitary, the 
other consisting of animals united in chains. The solitary indi- 
viduals are about an inch long, and have two long 
processes at the posterior end. These single ani- 
mals reproduce by budding, and form series of indi- 
viduals in small chains, the ani- mals being arranged 
in tworows. The chains grow to. the length of a 
foot or more, and contain twenty to thirty pairs 
of salpas.. Each of these connected individuals 
produces in turn a sin- gle egg, which becomes a 
single Salpa, and this again, like its grandmother, 
reproduces by bud- ding. Thus the animals are 
alike only in alter- nate generations. The natural- 
ist Chamisso, who discovered the relationship be- 
tween the two forms, expressed it as follows: a 
Salpa mother is not like its daughter or its mother, 
butresembles chain. its sister, its grandmother, and its grand- 
daughter. The single zodids liberate many colonies during the 
summer, which grow rapidly, and in the autumn the chains are 
exceedingly abundant. The Salpa chains swim about with a ser- 
pentine movement, and are beautiful, delicate objects with their 
transparent bodies banded with white, tinged with pink, and 
streaked with blue. 
SIMPLE ASCIDIANS 
These are solitary and usually fixed; they are never free-swim- 
ming, and when in colonies each animal has a distinct test. All 
the larger ascidians, or sea-squirts, belong to this group. 
Genus Molgula 
Body more or less globular, membranous, attached or free; 
orifices on very contractile tubes. 
M. manhattensis. Nearly globular when the tubes are contracted ; 
usually covered with bits of eel-grass, seaweeds, sand, etc.; surface a 
