A TELEOSTEAN FISH. 261 
. Camera-lucida sketch of the tail of a specimen of P. antarcticum, 1:05 cm. 
long. Notice the appearance of skleroblastic tissue, sk’, dorsal to the noto- 
chord, accompanied by a slight up-bending of the tip of the notochord. 
a, a fusion of cartilages marked a’ and a” in fig.2. 6, a hemal arch. 
c, a radial. 
. Tail of a specimen of P. antarcticum, 1:3 cm. long. Definite cartilaginous 
elements, ep, have been formed dorsal to the notochord, which has now 
a marked dorsal flexure. Notice the row of lateral-line sense-organs 
extending on each side along the trunk and on to the dorsal fin, marking 
its future mid-line. phy, posterior hypural. k, an abnormal piece of 
cartilage. 
. A whole mount of the tail of a specimen of P. antarctiewm, 1°55 cm. long. 
The dorsal flexure of the notochord has reached its maximum. Neural 
arches, na, have begun to appear. The figure shows three stages in the 
formation of a hypural. Anteriorly there is a heemal arch, behind it is 
another hemal arch with a radial, 7, at its distal end. The two elements 
have not begun to fuse. Behind these again is a hypural (for description 
of which see Stage III). 
. A reconstruction from a series of sections of the tail of a specimen of 
P. antarcticum, 1°8 cm. long. (Sections posterior to “dorsal hypural” 
lost. Tip of notochord and nerve-cord hypothetical.) The cartilaginous 
elements are represented as seen in a seetiou near the sagittal plane. 
Notice the fusion that has taken place between radial and hemal arch 
seen in fig. 5. 
. A reconstruction from a series of sections of the tail of a specimen of 
P. antarcticum 2°2 cm. long. Notice the anterior peg, p, of the “ ventral 
hypural” which passes between the notochord and caudal vein and 
artery, fusing with the proximal portion of the hypural in front of it. 
Notice also the cartilaginous elements, car, which later on give attachment 
to the anterior dorsal and ventral procurrent fin-rays. An asterisk marks 
the exit of the caudal artery and vein from the hemal arches. 
Puate If. 
. A dissection of an “odd tail” of Plewragramma antarcticum, probably 
2°8 cm. long. It shows the uniform nature of the “ dorsal hypural,” d, 
(the compound nature of which has been seen in previous figures). It 
will be noticed that the posterior neural arch, », is expanding at its distal 
extremity. 
. An antero-lateral view of a dissection of the notochord and cartilaginous 
elements of the posterior end of a specimen of P. artarcticum, 42 com. 
long. It was drawn under Zeiss binoculars with the aid of a camera 
lucida. Note the increase in development of the neural arches from 
before backwards. The sketch illustrates the way in which the neural 
arches grow over the segmental nerves. sp, backward growing spurs. 
g, gap between dorsal and ventral hypurals. 
. A latero-dorsal view of the specimen figured above (fiz. 9). It will give a 
better idea of the shape of the neural arches. e, f; the two halves of a 
neural arch. 
. A camera-lucida sketch of a dissection (mounted in balsam) of the noto- 
chord and cartilaginous elements of the posterior end of a specimen of 
P. antarcticum 45 cm. long. Notice the incipient division of the 
posterior neural arch into two. A considerable change in the shape of 
the two large hypurals has taken place (see text, p. 257). 
A dissection of an adult speeimen (16°5 cm.) of Plewragrammea antareticum. 
The tip of the notochord is represented as being naked. The attachment 
of the large hypurals is rather broken in this specimen (it had been 
devoured by a Seal), so that it is quite possible that the tip of the noto- 
chord was ensheathed by thin membranous bone. The drawing was made 
with the help of a camera lucida aud Zeiss binoculars. d, posterior or 
dorsal hypural. a, anterior or ventral hypural. 
. A dissection of a specimen of Trematomus newnesii, 6 cm. long (adult ?). 
It is given for comparison with fig. 12. The tip of the notochord is naked 
and extends out between the caudal fin-rays. 
. A diagram of the caudal skeleton of Trematomus borchgrevinki. 
18* 
