16 



THEORIES OF THE CCELOM 



tended blood -spaces of Mollusca and Arthropoda with tho 

 Vertebrate coelom, whilst he correctly identified with it the grer.t 

 body-cavities of Chaetopods and Echinoderms. 



The word " ccelom " was adopted by Haeckel's friend \\ .-id 

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

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

 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 coelom 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 scries of observa- 

 tions, which have ultimately led 

 to a view as to the essential nature 

 of the ccelom different from that 

 of Haeckel and Gegenbaur, already 

 existed before the word coelom 

 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 OK BAI.ANOGLOSSTJS IN OUtgl'OWth of the archeiltei'On of the 

 SAGITTAL SECTION TO snow THE ORKMN cm br V (see Fig. 2) whilst a SCCOnd 

 OF THE OKLOM AS THREE PAIRS OK *, . , . , , 



ENTKROOOCLOUH POVCHES. outgrowth gave rise to their ambul- 



c,, anterior, c,,, middle, C,,,, posterior acnil system ; and in 1869 Metsch- 



paiis of cu-ioniic pouches; </, arri.ni- nikoff (Mem. de 1'Acad. Imperiale 



iTii JT BateS "' fr 1n Km> l dcs Sciences de St. Petersbourg, 



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). Metsch nikoff 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 ccelenteric apparatus 

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



