
No. 428.] THE METAMORPHOSIS OF SISYRA. 619 
is forked, the outer branch of the fork being longer than the 
inner, and both curved inward toward the body. Between these 
two branches the second joint is attached (c and d, Fig. 5). 
The purpose of these inward-curving forks is probably to 
keep the respiratory filaments from too close contact with the 
body, and give them greater access to 
the currents passing through the pores 
of the sponge. It would seem that the 
first pair, having lost the fork at the 
terminal part of the first joint, have 
developed the hook-like projection 
nearer the base for a similar purpose. 
Two trachez can be partially traced 
in the alcoholic specimens, showing 
through the delicate outer membrane 
of the respiratory filaments. 
The mandibles and maxillae, to fit 
them for piercing organs, have attained 
a length nearly equal to that of the 
antennae (Fig. 4) and are joined to form two sucking tubes. In 
à cross section of these tubes (a, Fig. 6) the grooved edges are 
shown, by means of which mandible and maxilla fit each other 
closely. The grooved edges of both mandible and maxilla are 
finely serrated longitudinally, prevent- 
ing them from slipping one upon O a e 
another when they are used in punc- 
turing the sponge tissue. The two 
readily pull apart, showing that there 
is no adhesion of the chitin, but that 
they are merely apposed. As seen in 
Fig. 4, these sucking tubes are con- 
joined for nearly their entire length, 
being separated only at the tip and  jyax; 4 tendons; », m, points of 
near the base. After they enter the sachment of TEET 
head they unite in a Y-shaped joint, thus forming a single tube. 
This Y-shaped joint can be plainly seen on the underside of the 
head in the chitinous shell obtained by the use of caustic 
potash solution. After the junction the single tube passes on 
X 

filament of fifth pair. 

