A TELEOSTEAN FISH. ONS 
fused. Their proximal ends have grown till they now stand on 
the notochord. 
The hypurals are now beginning to expand laterally at their 
proximal ends, so as to form a broad seat for the convexity of the 
upturned notochord, so that the thrust of the tail is more widely 
distributed. Fusion has taken place between the hemal arch 
and radial (7.) described in Stage V. he epaxial elements 
behind the neural arches have undergone a certain amount of 
fusion, so that there is now a smaller posterior and a larger 
anterior cartilage. The caudal artery and vein are both forked 
at their posterior ends to pass round the large ‘ventral hypural,” 
which is not arched, to admit of their passage between it and 
the notochord. Fig. 6 is a reconstruction of this stage from a 
series of transverse sections. 
Stage VII (2-2 em.) (fig. 7),— Long narrow cartilaginous pieces 
(car.) have now made their appearance, one dorsally to the two 
posterior neural arches and the three original (apparently now two) 
epiural apophyses described above, and another ventral to the most 
anterior hemal arch. They give articulation to a dorsal and a 
ventral group of procurrent lepidotvichia. From the shape and 
position of this ventral piece of cartilage, it appears possible that 
it may be the homologue of the two radials or hypural apophyses 
which appeared just behind it and underwent fusion with two 
hemal arches. The anterior ends of both these new cartilages 
develop into two or three smaller and more or less separate 
cartilages. The anterior peg of the “ventral hypural” now 
extends between the proximal ends of the next anterior hypural, 
with which it eventually fuses, giving rise to the appearance in 
transverse section of a fusion of the halves of the arch themselves, 
and making in fact a small bridge, dorsal to the caudal artery 
and vein, which has rather a puzzling appearance. 
The division between the halves of the “dorsal hypural” 
(d, Pl. II. fig. 8) has now disappeared, or, in other words, the two 
uppermost hypurals have fused (Stage VIII), and a certain 
amount of absorption of the two large hypurals seems to be taking 
place, which, together with growths in other points, such as the 
posterior margins and the proximal ends, causes a considerable 
change in shape. Between Stages II and VII the rate of growth 
of the hypurals is greater than the rate of increase in girth of 
the notochord; but between Stages VII and X there is a reversal 
of this disparity which culminates in the condition where the 
notochord has the relatively enormous proportions so character- 
istic of the latest available postlarval stages of this fish. 
Stage VIII shows the first step in this inflation of the notochord, 
but here, as in later stages, the upturned tip or Chordastab 
is not affected. In this respect Teleosts show an important 
difference from Elasmobranchs (see Schauinsland, p. 462). Figs. 
9 and 10 ave drawn under the binoculars with camera lucida, 
and show a dissection of the posterior end of the notochord, 
nerve-cord, and cartilaginous elements of a fish 4:2 cm. long. 
