98 M. U.s.'=50>v's Zoolo(/ico-E)iihri/o(ii</i(((/ Inresfiijations. 



THE CEPHALOPODA. 



No group of Invertebrate animals possesses so high an 

 interest as the Cephalopoda with regard to the eoniplieation of 

 their bodily structure. And, in fact, since the time of Cuvier*, 

 who, taking the exact data of comjiarative anatomy into con- 

 sideratit>n, tirst sharply defined them and separated them from 

 the other classes of Mollusca, they have been })laced by most 

 zoologists t at the head of all Invertebrata. Some natural- 

 ists} who wished to see zoological clas^siiieation founded upon 

 embryological facts (at that time still little known and often 

 misunderstood) thought that it might be possible to separate 

 the Cephalopoda altogether from the MoUuscan type, and to 

 form a special type of them. Even before this peculiar 

 opinion was expressed, a special kind {evolutio radi'ata>^) of 

 the so-called unilateral development was established for the 

 Cephalopoda and some other Mollusca. Without denying 

 the merit of these conceptions as to the systematic position of 

 the Cephalopoda in the animal kingdom, which were valu- 

 able in their time, we may be allowed to put the question 

 whether we are sufficiently accjuaintcd with the most important 

 modes of development of the organism of the Cephalopoda, 

 and whether we are in a position, resting tipon embryological 

 facts, to state accurately the most sharply marked traits of 

 their phylogenetic connexion, not with all the other types of 

 the animal kingdom, but merely with the other classes of 

 Mollusca, as with the Gasteropoda, and especially with the 

 Pteropodail. If we look closely into this last highly important 

 scientific question, however, it appears that the positive facts 

 noAV known to us regarding the developmental history of the 

 Cephalopoda are far from sufficient, even ap])roximately, to 

 elucidate their genealogical relations. Notwithstanding the 

 interesting results which were to be expected from the inves- 

 tigation of the developmental history of as many species of 

 Cephalopoda as possible, we at present possess oidy three more 



♦ M^m. pour servir a Ihist. de I'Anat. des Molhisquos, 1817, M6m. i. 



t Lamarck, Hist. Nat. des Anim. sans Vert. 2"" edit. xi. p. 10/5 ; R. 

 Leuckart, Ueber die Morpbol. und die Venvandt.«cliaft.'?verliiQtn. der wir- 

 bellosen Thiere, 1848; Iluxley, Lecture.s on the Eleni. of Cotnp. Anat. 

 1804, p. 85 ; (iegenbaur, Vergl. Anal. I'te Auti. l)-(70, p. 78 ; Uackel, Gen. 

 Morpbol. Bd. ii. pp. cxv, 408 et seq. ; Clans, Gruudziige der Zoul. :^te Aufl. 

 187o, pp. 4;^, 44, 700 et seq. 



X \o^'t, Zool. Briefe, 1851, Bd. i. p. 2U8. 



§ Von Jiaer, " Beitr. zur Kenutn. der uiederen Tbiere.' Xova Acta &c, 

 xiii. pi. ii. \ii2~ ] Kolliker, Eutwickhuifrsgescb. der Copbalopoden, 1^44, 

 p. 175. 



II See Leuckart, /. c. p. 154 ; Gegenbaur, /. r. p. 47-» ; Ilackel, /. v. pp. civ, 

 cxv : Keferstein, Kla.'^.sen mid Ordii. der Weicbtbiere, p. 147-. 



