179 
think it probable that not only the one directive mesentery is sup- 
pressed but, on the right side, also the protomesentery 2. The 
long M-mesentery on the right side is then the M-mesentery in 
the first quartette, and the mesentery Mx an extra mesentery. 
The arrangement of the protomesenteries on the left side is cert- 
ainly normal. The irregularity in the development of the proto¬ 
mesenteries is here also accompanied by a suppression of the hypo- 
sulcus and hemisulci. 
In the second and third specimens (figs. 7, 8) the number of 
protomesenteries is normal, a short hyposulcus and well developed 
hemisulci are also present. The latter are filamentous but at least 
in the specimen 2, not furnished with a ciliated streak. In the 
second specimen the directive mesenteries are of usual structure 
(fig. 7), in the third specimen (fig. 8) they are anormal, the right 
directive mesentery is furnished with a rather long ciliated tract but 
of the ciliated streaks only one is developed, below the ciliated tract 
there is a rather well developed cnidoglandular tract. The left direc¬ 
tive mesentery agrees as to the filaments with the protomesenteries 
2 but are considerably longer than those. The rather short second 
protomesenteries (pj) resemble the older metamesenteries m, as 
far as the filaments are concerned. In the second specimen 
(fig. 7) the protomesenteries 2 are fertile, in the third (fig. 8) ste¬ 
rile. The third protomesenteries (ps) are of the usual structure 
and agree with the metamesenteries B and b. 
The metamesenteries are more typically developed but display 
also irregularities. In the first specimen (fig. 6) an extra mesentery 
X IS intercalated, for the rest the arrangement of the metamesen¬ 
teries IS MBmb. In the second specimen (fig. 7) two mesenteries, 
one m-mesentery and one B-mesentery, have arisen on the left 
side between the protomesentery 3 and the metamesentery Mi, 
on the right side two mesenteries are probably intercalated in the 
first quartette, the third metamesentery is namely a M-mesentery 
instead of a m-mesentery and the fith a m-mesentery, though the 
region of the craspedonemes of the ciliated tract is as usually longer. 
In the third specimen (fig. 8) two extra mesenteries, one m-mesen- 
tery and one b-mesentery, are situated in the second quartette on 
the right side. 
The M-mesenteries are in each quartette aiways longer than 
12 * 
