1220 
SCANDINAVIAN FISHES. 
advances on the ventral margin forward to the atrio- 
pore, but there it has a double series of supporting 
cartilages (fin-rays), instead of the single row in the 
other parts of the vertical fin. In front of the atrio- 
pore are the two lateral ridges (metapleures) answering 
to the first rudiment of or at least foreshadowing la- 
teral extremities, whether they represent both extremital 
pairs of the other vertebrates, being not yet differen- 
tiated into an anterior and a posterior pair, or correspond 
to the pectoral fins alone, in which case the double 
series of rays in the atrio-anal fin would appear to have 
some homology with ventral fins. But as yet they are 
merely steering organs. This is a function, however, 
which is for the most part retained by the unpaired fins 
of the back and belly, and indeed by the lateral fins, even 
in the highest evolutional grades of the piscine type. 
The structure and development of Branchiostoma 
have now shown us a creature with the vertebrate di- 
vision of the body into a neural and a haemal canal, 
with a notochord and the membranous elements of an 
axial skeleton between and around those canals, and 
with the vertebrate type expressed in musculature, 
spinal nerves, respiratory, excretory, and generative 
organs. But in other respects we have seen an asym- 
metry, partly persistent, partly temporary, which is 
distinctly foreign to the vertebrates, but common among 
the mollusks; the respiratory organs present a striking 
resemblance to those of the Ascidians; and the most 
important organs of nutrition and circulation, though 
comparable with the vertebrate type, retain much of 
their structure in the worms. Hence the great morpho- 
logical interest attached to this genus, which in other 
respects is not especially remarkable. Its forms are so 
similar that in his famous Catalogue Gunther recog- 
nised only a single species. Sundevall, however, had 
already (1852 — 53) distinguished between three species, 
with characters derived from the form of body and the 
number of myomeres. At a more recent date Gunther 
has decided, basing his conclusions in the main on the 
same characters, that six different species deserve re- 
cognition within the genus. Only one of these belongs 
to the seacoasts of Europe. 
THE LANCELET (sw. lansettfisken). 
BRANCHIOSTOMA LANCEOLATUM. 
Plate L1II, fig. 6. 
Greatest- depth of the body about 9 — 10 l l 2 % a , greatest breadth ( thickness ) thereof about 6 — 8 % b , of the length 
of the same. Distance from, the tip of the snout to the posterior limit of the mouth aperture about 8 % e , to the 
atriopore about 70 % d , to the vent about 88 %\ of the length of the body. Number of myomeres 60 — 62, 
11 — 13 situated behind the vent. 
Syn. Limax lanceolatus, Pall., Spicil. Zool., fasc. X, p. 19, tab. 
I, fig. 11; ( lanceolaris ), Naturg. Merkw. Th., Samml. X, 
p. 24, tab. I, fig. 11; Yakr. (Amphioxus lanceolatus ), Brit. 
Fish., ed. 1, vol. II, p. 468; Fr., Vet. Akad. Handl. 1838, 
p. 336, tab. 4, fig. 3; Sundev., F., Fork. Skand. Naturf. 
Kbhvn 1840, p. 280; Sundev., C. J., Arsber. Zool. Framst. 
1840 — 42, Vertebr., p. 287; (Avers. Vet. Akad. Fork. 1852, 
p. 148; 1853 ( Branchiostoma ), p. 12; Quatref., Ann. Sc. 
Nat., ser. 3, Zool., torn. IV, p. 197, tabb. 10 — 13; Kr., 
Damn. Fisk., vol. Ill, p. 1087; Nilss,, Skand. Fna, Fisk., 
p. 753; Couch ( Amphioxus ), Fish. Brit. Isl., vol. IV, p. 
415, tab. CCXLVIII, fig. 4; Gthr ( Branchiostoma ), Cat. 
Brit. Mus., Fish., vol. VIII, p. 513; Rep. Zool. Coll. Alert 
(Brit. Mus. Nat. Hist. 1884), p. 32; Coll., Fork. Vid. Sels. 
Ckrnia 1874, Tillsegsk., p. 222; N. Mag. Naturv., Bd 29 
(1884), p. 123; Malm, Gbgs, Boh. Fna, p. 641; Winth., 
Naturli. Tidskr. Kblivn, ser. 3, vol. XII, p. 62; Mor., Hist. 
Nat. Poiss. Fr., torn. Ill, p. 618; Storm, N. Vid. Sels. 
Skr. Trondhj. 1883, p. 48; Day, Fish. Gt. Brit., Irel., vol. 
II, p. 366, tab. CLXXIX, fig. 4; Ptrn, Vid. Meddel. Naturli. 
For. Kbhvn 1884—86, p. 160; Retz., G. ( Amphioxus ), 
Biol. Unters., N. F., vol. II, p. 29, tabb. XI— XIV; Car. 
( Branchiostoma ), Prodr. Fnce Medit., vol. II, p. 498. 
Branchiostoma luhricum, Costa, Cenni Zool. (1834), p. 49; 
Fna Regn. Nap., Pesci, part. II, tav. XXX; J. MOll., Abk. 
Akad. Wiss. Berk 1842, Pkysik. Abh., p. 79. 
Gasterobranchus glutinosusf, Rasch, Mag. Naturv. Chrnia, Bd 
12 (1836), p. 325. 
" 8'9 — 10‘6 % according to our measurements of specimens 43 — 48 mm. long. 
6 5'8 — 8‘3 % according to our measurements. 
7 ' 5 8’8 % ,, ,, ,, ,, 
67 —71 % „ „ „ 
' 86-5—90 % „ „ „ 
11 
