402 ZOOLOGY. 
pears within its body. We will now briefly trace the devel- 
opment of the chain-salpa, condensing Brooks’s statement. 
The aforesaid tube is at first simply a cup-like protrusion of 
the outer tunic into the cellulose test which now surrounds 
the embryo ; the cavity of the cup is an offshoot from the 
sinus-system, the blood passing in and out of it. A small 
bud-like protrusion now appears upon the surface of the per- 
icardium, and lengthens to form a long rod or stolon, ex- 
tending across the sinus and projecting into the cavity of the 
cup. At about this period a long, club-shaped mass of pro- 
toplasm appears within each of the sinus-chambers of the 
tube, and soon after the outer wall is constricted at regular 
intervals, each segment being destined to form the outer tu- 
nics of the chain-salpz, the constrictions indicating the 
bodies of the latter. 
By the deepening of these constrictions, each of the 
sinus-chambers, which are diverticula from the body-cav- 
ity of the solitary Salpa, becomes divided up to form the 
body-cavities of the Salpz on one side of the chain. From 
the central tube of the stolon arises a row of buds on each 
side, which become the branchial and digestive organs of the 
Salpze on each side of the chain ; while a similar double row,. 
upon the other edge, gives rise to the ganglia. The club- 
shaped organs within the sinus-chambers become divided up 
into single rows of eggs, one of which passes into the body- 
cavity of each chain-salpa at a very early period of develop- 
ment. 
Thus, as Huxley states, budding occurs, not from the outer 
wall alone, as in Hydroids and Polyzoa, ‘‘ but, from the first, 
several components, derived from as many distinct parts of 
the parental organism, are distinguishable in it, and each com- 
ponent is the source of certain parts of the new being, and 
of these only.” Prof. Brooks adds that while these changes 
are going on the constrictions on the surface deepen, the 
wall protruding from them, and each is soon seen to mark 
off, on cach side of the stolon, the body of a young Salpa,. 
which soon becomes visible to the naked eye. They do not 
increase in size gradually from one end of the stolon or tube 
to the other, but develop in sets of from thirty to fifty each, 
