SCANDINAVIAN I-ISHKS. 



advances on tlie \entral luar^uin Ibi'ward \o tlic atrio- 

 j)ore, l)ut tliere 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- 

 ])ore are the two lateral ridges (raetaploures) answering 

 to the first rudiment of or at least foreshadoAving la- 

 teral extremities, wliether they represent both extreinital 

 pairs of the other vertebrates, being not j'et differen- 

 tiated into an anterior and a posterior |)air, or correspond 

 to tiie pectoral fins alone, in wiiicli case the doul)le 

 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, 

 \\iiic!i is for the most part retained by the unpaired fins 

 of the back and belly, and indeed by tlie lateral fins, even 

 in the highest evolutional grades of the piscine type. 

 The structure and development of Branchiostoma 

 have now sliown us a ci'eature with the vertebrate di- 

 vision of the body into a neural and a hfemal canal, 

 witli 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 asjnu- 

 metry, partlj' persistent, partly temporary, A\-hich is 

 distinctly foreign to the vertebrates, but common among 

 tlie mollusks; the respiratory organs present a striking 

 resemblance to those of the Ascidians; and tlie most 

 important organs of nutrition and circulation, though 

 coni|)arable with the vertebrate type, I'etain 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 GCnther recog- 

 nised only a single species. Sundevall, however, had 

 already (1852 — 53) distinguished between three species, 

 with characters deri\ed from the form of body and the 

 number of myomeres. At a more recent date Gi'NTHEii 

 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 Ijelongs 

 to the seacoasts of Europe. 



THE LANCELET (sw. lansettfisken). 

 BliAXCHIOSTOMA LANCEOLATUM. 



Plate LIII. tig. 6. 



Greatest depth of the body about 9 — 10\uj %", greatest breadth (thickness) thereof abont 6 — 8 %'', of the length 

 of the same. Distance from the tip of the snout to the posterior limit of the month aperture about 8 %% to the 

 afriopore ahont 70 %'' , to the rent about 88 %' , of the length of the bodg. Number of mgomeres C>() — €2, 



n — 13 situated behind tlie rent. 



Si/n. Limax lanceolatus, Pall., (Hjiidl. Zool., fasc. X, p. 19, taVi. 

 I, fig. 11; (lanceolaris), Naturg. Merkw. Th., Samml. X, 

 p. 24, tab. I, tig. 11; Yakr. {Amphio.vus lanceolatus), Brit. 

 Fish., ed. 1, vol. II, p. 4GS; Fr., Vtl. Akatl. Handl. 1838, 

 p. 336, tab. 4, fig. 3; Sundicv., F., Forb. Skand. Naturf. 

 Kbhvn 1840, p. 280; Sundev., C. J., Arsber. Zool. Framst. 

 1840—42, Vertebr., p. 287; Ofvers. Vet. Akad. Forb. 1852, 

 ]i. 148; 1853 {Branchiostoma), p. 12; Qi'atref., Ann. Sc. 

 Nat., ser. 3, Zool., torn. IV, p. 197, tabb. 10—13; Kr., 

 Danm. Fisk., vol. Ill, p. 1087; Nilss., -S*<i/«/. Fiia, Fisk., 

 \i. 7.53; Couch {A7nphioa:iis), Fish. Brit. /«/., vol. IV, p. 

 415, tab. CCXLVIII, fig. 4; Gthb (Branchiostoma), Cat. 

 Brit. Mus., Fish., vol. VIII, p. 513; Rep. Zool. Coll. Alert 

 (Brit. Mils. Nat. Hist. 1884), ]>. 32; Coll., Forb. Vid. Rels. 



8'9 — 10'6 % according to our iiieasurenients of .specimens 43- 



5'8 — 8'3 % according to our iiiensurenients. 



7-5— 8-8 % .. „ „ 



C7 —71 % „ „ „ „ 



8G-5— 90 % „ „ „ 



Chrnia 1874, Tillaigsb., p. 222; N. Mag. Natiirv., Bd 29 



(1884), p. 123; Malm, Gbgs, Boh. Fna, p. 641; Winth., 



Natiirb. Tidskr. Kbbvn, ser. 3, vol. XII, p. G2; MoR., Hist. 



Nat. Foiss. Fr.. toin. Ill, p. 618; Storm, N. Vid. Sels. 



Skr. Trondbj. 1883, p. 48; Day, Fish. 6t. Brit., frel., vol. 



II, p. 306, tab. CLXXIX, fig. 4; Ptrn, Vid. Meddel. Natiirb. 



Fur. Kbhvn 1884 — 86, p. 160; Retz., G. (Amphio.riis). 



Biol. Futers., N. F., vol. II, p. 29, tabb. XI— XIV; Car. 



(Branchiostoma), Prodr. Fna- Medit., vol. II, p. 498. 

 Branchiostoma lubricum, Costa, Oenni Zool. (1834), p. 49: 



Fna Regn. Nap., Pesci, part. II, tav. XXX; J. Mt'Li,., Abli. 



Akad. Wiss. Berl. 1842, Physik. Abh.. p. 79. 

 Gaslerobranclnis glutitwsus.', Rasch, Mag. Natiirv. Cbrnia, Bd 



12 (1836), p. 325. 



lona 



