i6 



THEORIES OF THE CCELOM 



r\C, 



tended blood -spaces of Mollusca and Arthropoda with the 

 Vertebrate ccelom, whilst he correctly identified with it the great 

 body-cavities of Cheetopods 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 " Grundzuge der ver- 

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

 says in regard to the coelom of Mollusca : " As a' rule the vascular 

 system is freely connected with the coelom, which therefore forms 

 a portion of the haemal system." 



And again, in relation to the coelom 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 fluid 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 different from that 

 of Haeckel and Gegenbaur, already 

 existed before the word ccelom 

 itself was coined. As far back as 

 1864 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 [great body -cavity of those 

 animals developed as a pouch-like 

 FIG. 4. LARVA or BALANOGLOSSDS IN outgrowth of the archenteron of the 



SAGITTAL SECTION TO SHOW THE ORIGIN em bryo (see Fig. 2) whilst a SBCOnd 

 OF THE CCELOM AS THREE PAIRS or . ' , . . . 



BSTEJMXXELOUS POUCHES. outgrowth gave rise to their ambul- 



c,, anterior, Cn, middle, Cm, posterior acral system; and in 1869 Metsch- 



pairs of coelomic pouches; d, archen- n ik o ff (Mem. de 1'Acad. Imperiale 

 teron. (After Bateson. from Korschelt j & j Oi T> *. i 



and Heider.) " es Sciences de St. retersbourg, 



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). Metschnikoff has further the credit of having, in 

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

 Leuckart's theory of the relationship of the coelenteric apparatus 

 of the Enteroccela to the digestive canal and body-cavities of 



