226 



5) Transference by secondary adaptation of the remnant of mono- 

 cytic ingestive cells (fat absorbers) to the vascular system. 



All these several processes depending upon general laws and 

 upon fundamental properties and activities of protoplasm will proceed 

 upon parallel lines in all the great branches of the Metazoa. 



One need not recapitulate in detail the morphological facts of 

 the origin and fate of the coelom shewn especially in the developement 



Fig. 4. 



Excf'efoiy 



rolyc-ytie Digcr^iive Cavity 



Polycyîi« 



eg-cffirive 

 dpertur«. 



Excreior, 

 celJs. - 



■fionocyti 



t-gestîve 



Fig. 4. Longitudinal section throug a triploplastic coelomate Metazoan with 

 two pairs of mesoblastic pouches, showing the stages in evolution of excretory cells 

 around the monocytic and polycytic egestive apertures. This form with a coelomic 

 prostomial area probably represents the primitive ancestor of the Coelomata. Endo- 

 derm black, mesoderm shaded, ectoderm white. 



of Peripatus ^^ and other forms and in the morphological comparison 

 of the coelom ^2 in different types which is well known to all zoologists. 



So far as I am aware, no theory prior to this has been suggested 

 to account for the facts from a physiological basis. 



Returning for the moment to the consideration of excretion, reasons 

 have been given for connecting excretion primitively with the general 

 ectoderm , and the organs for excretion of salts and water appear to 

 remain in this diffuse condition even in the highest Vertebrates*'^, 

 in the case of respiration the respiratory organ is formed in each group 



6' In Peœipatus »the functions of a perivisceral (or body) cavity are discharged 

 by the vascular system, in which indeed the coelom is contained«. A. Sedgwick, 

 a J. M. S. XXVIII. —A. Sedgwick, Developement of Peripatus. Q. J. M. S. 

 XXV etc. 



62 E. li. Lankcstcr, Q. J. M. S. XXXIV. 



6'' In frog, waste respiratory pigment is got rid of through the skin (melanin)- 

 J. H. List, Biol. Centralbl. 1890 etc. 



