Tl DOLIOLUM- 
LIFE-HISTORY 99 
oozooid, and are sacrificed for the benefit of the rest of the 
colony. They serve merely to aid in respiration, and to provide 
the food for the nurse and the median buds. Their development 
is arrested; they have the body elongated dorso-ventrally with a 
large funnel-like branchial aperture (Fig. 60, F), and the 
musculature is very shghtly developed. 
(2) Some of the median buds become foster forms (“ phoro- 
zooids ”), which, like the preceding trophozooids, do not become 
sexually mature, but, unlike them, are eventually set free as 
eask-shaped bodies having the Doliolwm appearance, with eight 
encircling muscle-bands, and having, moreover, a ventral out- 
growth (not a stolon), which is formed of the stalk by which 
the body was formerly attached to the dorsal process of the 
oozooid, On this ventral outgrowth the “ gonozooids” (3) are 
attached while still very young buds, and after the phorozooids 
are set free these reproductive forms gradually attain their com- 
plete development, become sexually mature, and are eventually 
separated off, finally losing all trace of their temporary connexion 
with the foster-forms. They resemble the foster-forms in having 
a cask-shaped body with eight muscle-bands, but differ in the 
absence of a ventral process, and in having the sexual repro- 
ductive organs fully developed. 
Occurrence.—The best-known member of the genus is 
Doliolum tritonis, Herdman, which was captured in the tow-nets 
in thousands by Sir John Murray during the cruise of H.M.S. 
“Triton” in the summer of 1882 in the North Atlantic. Since 
then that species, or the closely allied D. nationalis, Borgert, have 
been found on more than one occasion in the English Channel 
and other parts of our south-west coast, and so Doliolum may 
be regarded as an occasional member of the British surface 
fauna. 
It is probable that the occasional phenomenal swarms gf 
Doliolum which have been met with in summer in the North 
Atlantic are a result of the curious life-history which, under 
favourable circumstances, allows of a small number of oozooids 
producing from minute buds an enormous number of phorozooids 
and gonozooids. 
As the result of the careful quantitative work of the German 
“ Plankton ” expedition, Borgert thinks that the temperature of 
the water has more to do with both the horizontal and the 
