210 



In the Echinoderma24 the ek-phorocytes appear to leave the or- 

 ganism by any part of the outer layer which is suitable, such as the 

 branchiae. They leave the coelom and wander through its outer wall 

 and the ectoderm to the exterior. Although Durham shewed only the 

 egestion of foreign particles from the coelom, the whole circuit may 

 be followed out by feeding Asterias with pigments , which are then 

 ingested through the endoderm layer, appear in the coelom, enclosed 

 in leucocytes and eventually are expelled through temporary pores in 

 the branchiae. 



In the sponges 25 metamorphosed choanocytes leaving the ingestive 

 layer pass into the mesogloea and through the ectoderm to the exterior, 

 carrying with them the egestive residua. 



We thus see that although, in the Echinoderma, the coelom is 

 definitely established yet the monocytic egestion is of the same diffus- 

 ed type as in the sponges. There are no definite egestive openings 

 from the coelom to the exterior. 



In the higher coelomata, the coelom opens, however, by definite 

 apertures to the exterior, (coelomic pores, nephrostomes) and it is 

 more than probable that these are definitely connected with the mono- 

 cytic egestive function. 



The evidence for this statement lies under several heads: 



1) Direct evidence of egestive cells carried to exterior by ne- 

 phridia. 



2) Relationship of the sexual cells, or gonocytes. 



3) The consideration of cases in which no ciliated internal aper- 

 tures are present, either undeveloped or lost. 



That solid particles are borne to the exterior through the nephri- 

 dia of Lumbricus is a demonstrable fact 26 and it has also been shewn 

 that ingestive cells from the typhlosole wander into the coelom and 

 after conducting monocytic egestion, are carried tho the exterior to- 

 gether with the waste residua by the nephridia^^. (Fig. 3.) 



Again, in the Capitellidae^s though the nephrotomes are present 

 yet the nephridia in some cases terminate in the skin, and are not 

 carried direct to the exterior. 



24 H. E. Durham, Trans. Royal Society. 1887. 



25 A. T. M. loc. cit. 



26 » When a worm has been made to eat powdered carmine, the passage 



from gut to yellow cells, from yellow cells to body-cavity, and thence out by the 

 excretory tubes, has been traced«. J. A. Thomson, Outlines of Zoology. 



27 Kükenthal, Jena Zeits. XVIII, 1885. 



28 H. Eisig, Fauna u. Flora G. v. Neapel XVI. 1887. 



