20 
into the muscles and did not reach the vertebral column; the mouth 
and feet were turned towards the surface of the fish. The o ther, 
figured on PI. II, Figs. 16—18, had an external part of only 1 mm., 
peeping out of a pit in front of the dorsal fin of a Scop. glac. of 
25 mm. length. It has pierced the whole musculature and reached 
between two ribs through the peritoneum, on the inside of which 
the mouth could be seen; the feet looked towards the vertebral 
column. The total length is 4 mm.; the cephalothorax is about 
1 mm (0,96 mm.), the 3-segmented abdomen 0,240, the remaining 
ca. 3 mm. are almost entirely made up by the genital segment; the 
latter is densely striated transversely, and by a very feeble furrow 
indistinctly marked off from the end segment, carrying the small 
furcal appendages devoid of setæ. The genital openings are recogniz- 
able at the posterior boundary of the genital segment. Except the 
elongation of the genital segment and the reduction of the jostrum 
the shape of the animal is that of the stage inside the oldest 
pupa E. The details of the strengthening ridges of the cephalo¬ 
thorax and antennæ are the same through all stages, also those on 
the sipho; but the mandibular palp of the larva and pupæ appears 
now to have vanished. 
The third specimen shows a step further towards the final 
shape (cfr. PI II, Figs. 19—21). It projected in front of the dorsal 
fin of a fish of 25 mm. length; the internal part perforated the 
muscles, passed close to the vertebral column between two ribs 
into the abdominal cavity, the mouth lying close to the left side 
of the small intestine at the origin of the hindmost pyloric appendage. 
The total length is 6 mm.; the cephalothorax 0,96 mm., the abdomen 
0,277 mm., the rest ca. 5 mm. The genital segment is still more 
elongated, and more swollen posteriorly than in the former, the 
greatest diameter being 0,320 mm. while that of the cephalothorax 
is 0,40. Between the genital openings is seen a chitinous spot, 
probably where the copulatory openings are obliterated. The most 
marked difference from the two preceding specimens is that the 
lateral processes of the cephalothorax have appeared in the shape 
