i6 



THEORIES OF THE CCELOM 



tended blood -spaces of Mollusca and Arthropoda with the 

 Vertebrate coelom, whilst he correctly identified with it the great 

 body-cavities of Chretopods and Echinoderms. 



The word " ccelom " was adopted by Haeckel's friend and 

 colleague in the University of Jena, Carl Gegenbaur. In the 

 second edition of his masterly treatise, the " Grundziige der ver- 

 gleichenden Anatomie" (English edition 1878, p. 367), Gegenbaur 

 says in regard to the ccelom of ^lollusca : " As a" rule the vascular 

 system is freely connected with the coelom, which therefore forms 

 a portion of the hiemal system." 



And again, in relation to the ccelom of Arthropoda, he writes 

 (p. 278 of the same work): "The ccelom is found in all the 

 Arthropoda, and forms a portion of the blood-vascular system, so 

 that the peri-enteric fluid found in many Vermes as a Huid different 



from the blood, is represented in 

 the Arthropoda by the blood 

 itself." 



The first of the series of observa- 

 tions, which have ultimately led 

 to a view as to the essential nature 

 of the coelom diflerent from that 

 of Haeckel and Gegenbaur, already 

 existed before the word ccelom 

 itself was coined. As far back as 

 186-4 Alexander Agassiz (Embryo- 

 logy of the Starfish, in Contri- 

 butions to the Natural History 

 of the United States, vol. v. 1864) 

 showed in his account of the de- 

 velopment of Echinoderma that 

 the I great body - cavity of those 

 animals developed as a pouch-like 

 Fio. 4. — Larva of BALANooLossns is outgrowth of the archentcrou of the 



Sagittal Sectio.n to show the Orioin embrVO (sce Fig. 2) whilst a SCCOud 



OF THE CCKLOM AS TuREB PaIRS OF ,' \ • ^ ^\ • ll 



ENTERococLots PotcHEs. outgrowth gavc rise to then- ambul- 



fi, anterior, fa, iniiUiie, Cm, posterior acral systcm ; and in 1869 Metsch- 



pairs of c.iomic iwuches ; </, arciien- nikotf (Mcm. dc I'Acad. Imjieriale 



teroii. (After liateson, from Korschelt i o- ic<i."r»i.i 



and Ueider ) "^'^ Scieuccs de St. i etcrsbourg, 



series vii. vol. xiv. 1869) con- 

 firmed the observations of Agassiz, and showed that in Tornaria 

 (the larva of Balanoglossus) a similar formation of body- 

 cavities by pouch - like outgrowths of the archenteron took 

 place (Fig. 4). Metschnikofl' has further the credit of having, in 

 1874 (Zeitsch. wiss. Zoologie, vol. xxiv. p. 15, 1874), revived 

 Leuckart's theory of the rolatiuiiship of the civlenteric apparatus 

 of the Enteroctela to the digestive canal and bodv-cavities of 



