Emhryologij of Saljpa. By W. K Brools. 1 1 
become united to the inner surface of the outer tunic. (Fig. 
VIIL, m.) 
The sides of the mid-atrium become united at two points, one 
on each side, with the posterior surface of the branchial sac, and as 
the atrial and branchial tunics are free from each other between 
these regions of union, a median longitudinal sinus is thus formed 
which is the " gill " or " hypopharyngeal band." The central 
portions of the two regions where the tunics are united, are soon 
absorbed, and a single branchial slit is thus formed on each side of 
the gill. 
The earliest stages in the formation of the atrial chamber were 
not observed, but nothing was seen which seemed to indicate that 
it is formed, as in most Tunicates, by tubular invaginations of the 
outer wall of the embryo. 
The cavity of the oesophagus is a prolongation of that of the 
branchial sac, and was in direct communication with this at the 
mouth when first observed. The stomach is formed as a diverti- 
culum from the side of the oesophagus, and the cavities of the two 
were connected at all the periods observed, but the cavity of the 
intestine originates independently, and at first is closed at both 
ends ; the partition between it and the stomach disappears first ; 
that at the anal or atrial end persists some time longer. 
The few facts which I have been able to add to what is known 
of the development of the Salpa-chain relate, for the most part, to 
the earliest stages in the development of this, which has always 
been considered the sexual generation ; and seem to prove that the 
solitary Salpa is the female, and the chain Salpa simply the male, 
which does not reproduce, but merely serves to fertilize and nourish 
the egg, so that we have, not an alternation of generations, but a 
very remarkable difference in the form and mode of origin of the 
two sexes. 
The tube or stolon which is to form the chain first appears as a 
protrusion of diverticulum from the outer or muscular tunic of the 
solitary Salpa, directly opposite the heart ; this protrusion rapidly 
increases in length, and soon presents the form of a long tube 
closed at its distal end, projecting into the test, and with its cavity 
in direct connection with the cavity of the sinus system (the body 
cavity) of the solitary k^'alpa, so that the blood of the latter enters 
and circulates freely within it. (Fig. X.) 
A second tube with very thick walls and a very narrow cavity 
now grows out from the pericardium, crosses the sinus and pene- 
trates the cavity of the outer tube almost to its tip or blind end, 
and soon becomes flattened and its edges unite with the walls of 
the outer tube, which thus becomes divided into two chambers, 
which are entirely separate from each other except at the tip. The 
blood now passes into one of these chambers at its base, and is 
