278 
PACIFIC SCIENCE, VoL VIII, July, 1954 
In many species, the presence of depressions 
and elevations is entirely accidental, due prob- 
ably to the convulsive contractions of the 
muscles at death. In my opinion the presence 
of elevations and depressions in a soft test 
(with the exception of distinct ridges and 
grooves) is in general without value as a 
character for species determination. There do 
seem to be a few exceptions, however, i.e., 
Pegea confoederata and Ritteriella amboinensis 
agg- 
The asymmetric nature of aggregate indi- 
viduals of salps is shown not only in the 
arrangement of muscles, attachment organs, 
and end projections but also in the sculpture 
of the test when it is stiff and has permanent 
structures (Stiasny, 1926; Ihle, 1937-39). 
In some species, such as Thalia democratica^ 
there are two basic body forms: one has a 
relatively thick test, prominent ridges and 
grooves, and wide muscle bands; the other 
has a thin test, ridges weak or absent, non- 
permanent elevations and depressions, and 
narrow muscles. 
Van Beneden and de Selys-Longchamps 
(1913) {fide Stiasny, 1926) and Stiasny showed 
that there had been entirely too much reliance 
on muscle arrangement for differentiating the 
various species. Nevertheless, muscle arrange- 
ment is one of the most important recogni- 
tion features. In order to determine some 
species, however, it must be combined with 
other features. 
MORPHOLOGY 
With the exception of Traustedt (1885), 
Brooks (1893), van Beneden and de Selys- 
Longchamps ( 1913 ) {fide Brien, 1948), and 
Stiasny (1919, 1926), all investigators have 
described the test only incidentally, their work 
being primarily concerned with the muscular 
arrangements of the various species. The only 
considerable contribution to the knowledge 
of test structure was made by Stiasny (1926). 
As he showed, the great difficulty encountered 
in the study of the test is its almost complete 
agreement in refractive index with water. 
Some salps have tests with ridges and grooves 
that can be seen under water, but the test of 
most shows little or no opacity. Hence, almost 
all investigators have completely disregarded 
the test in their researches. Traustedt (1885) 
and Brooks (1893) described the test in a 
few species, and Brooks recognized a basic 
plan in the test that fits some salps, especially 
the solitary forms. This plan was named 
Brooks’ rule (Regel von Brooks) by Stiasny 
(1926), and he applied it to many forms. Sti- 
asny also clarified the rule and stated it as 
follows : 
. . . finden wir regelmassig in der Mitte der 
Dorsalseite eine (tiefe) Langsfurche, beiderseits 
begrenzt von vorspringenden kiel-annlichen 
Kanten, an den seiten des Mantels vorsprin- 
gende scharfe Kanten oder Fliigelartige Ver- 
breiterungen; auf der Ventralseite ist die Testa 
dick, mit einem medianen und 2 lateralen 
Kielen. 
Stiasny also set up a scheme of nomencla- 
ture for test structure which is followed here 
although some of his terms have been changed. 
The result is a combination of his terms, of 
those used by Delage and Herouard (1898), 
and some additions. It is believed that the 
terminology used here is both clearer in mean- 
ing and easier for use in descriptions. The 
resulting scheme is shown in Figure 1. 
The following terms are used to describe 
the test: 
test~thQ outer tunic or covering over the 
epidermis 
mantle — the epidermis and associated tissues; 
the term does not refer to the test 
ridge— 2 ^ distinct elongate bulge, triangular in 
cross section 
groove— 2 . distinct elongate, angular invagina- 
tion 
elevation — a rounded, elongate bulge 
depression— 2 . rounded, elongate invagination 
swelling— 2 . prominent, nonelongate, rounded 
bulge 
cavity— 2 X\g concavity of the internal surface 
of the test 
