211 



cm. 



2) The origin of the sexual cells in Proterospongia is from the 

 transformed and immigrating flagellated cells at the exterior and these 

 eventiiallv leave the ^. , 



•' Fig. 3. 



colony as sexual ele- 

 ments ^9 so that in ori- 

 gin and fate they cor- 

 respond with primitive 

 ingestive cells , and 

 again in sponges ^o the 

 gonocytes are not re- 

 cognisable from the 

 ingestive amoebocytes 

 and suffer the same 

 emigrant fate. 



From these and 

 other examples we may 

 conclude that: 



(a) Gonocytes and 

 ek-phorocytes belong 

 primitively to the same 

 layer (ingestive area), 

 both phylogenetically 

 and ontogenetically, the one charged with reserve material the other 

 with digestive residua. 



(b) Their subsequent course through the organism is similar. 

 Hence there is every probability in favour of supposing that the 



apertures which we know to serve for the discharge of the gonocytes 

 will also be found to subserve the same function for the ek-phorocytes. 



Most authorities agree that the mode of dehiscence of ova through 

 the nephridia (nephrodinic) is a very primitive method and that the 

 evolution of separate sexual ducts (idiodinic) is a secondary adaptation. 



Thus the nephridia are known to function as gonaducts in many 

 primitive Coelomata such as Archi-annelida^', Gephyrea ^^^ Polychaeta, 

 etc. and the history of the nephridial funnels in the Vertebrata 33 points 

 to a secondary separation of the two functions. 



29 W. S. Kent, loc. cit. 



30 »New individuals are produced from the union of ova and spermatozoa, 

 which develope from wandering amoeboid cells in the mesoderm«. W. J. Sollas, 

 Encycl. Brit. »Sponges« 1885. 



31 S. F. Harmer, Journ. Mar. Biol. Assoc. N. S. Vol. I. No. 2. 



32 See Text-books uponSipunculus, Echiurus, Arenicola, etc. Seealso A. Hub- 

 r e e h t, Niederlandsche Arch, f . Zool. 1881 upon the Amphineura Compare also Sagitta. 



33 Rückert, »Entwicklung der Excretionsorgane«. Ergebnisse der Anat. 

 und Entw. I. 1891. 



Fig. 3. Transverse section of triploblastic coe- 

 lomata Metazoan with polycytic processes and mono- 

 cytic ingestive into the coeloniic digestive tract and 

 egestive through the nephridial apertures, cm Coelom 

 with nutritive fluid (dottet), hm haemocoele. iip ne- 

 phridial opening. 



