INTRACELLULAR DIGESTION OF INVERTEBRATES. 9 1 



speaks much more precisely. He states that in these sponges 

 the ectoderm is capable of taking up foreign particles, but not 

 of digesting them, the ingested matter being simply passed on 

 to the wandering cells of the mesoderm. However plausible 

 this view may seem, it appears, from Von Lendenfeld's state- 

 ments, to need confirmation. 



My own researches, conducted on Ascetta primordialis 

 and Halisarca lobularis, two sponges with strongly deve- 

 loped ectoderm, gave a negative result. I have lately re- 

 examined the last-named species, but again unsuccessfully : 

 particles of carmine suspended in water were taken in large 

 quantity into the entoderm and mesoderm cells ; but the ecto- 

 derm remained entirely free from them. 



From this I can only infer that, however probable a priori 

 the ingestion of food by ectoderm cells in sponges may be, it 

 is at present by no means proved. More favorable objects 

 for these researches are the true Coelenterates. A digestive 

 ectoderm has, as far as I am aware, been described in only a 

 single one of these. Merejkowsky,! in describing a Bougain- 

 villea in which the alimentary canal was rudimentary, has put 

 forward the supposition that in this Medusa the food was taken 

 in entirely by ectoderm : but he most carefully asserts that he 

 never found solid particles in the ectoderm of the abnormal 

 Bougainvillea, which he supposes to be nourished entirely by 

 organic matter in solution in the sea water. 



It has long been known that the ectoderm of hydroid polyps 

 protrudes pseudopodia, which frequently anastomose to form a 

 kind of Plasmodium; and it occurred to me that these pseudo- 

 podia might have the function of picking up food particles. I 

 have, so far, been able to verify this supposition only in the 

 single case of the so-called nematocalyces of Plumularia. I have 

 worked with P. setacea, Ellis, and with a species bearing very 

 large gonophores, and nearly allied to P. halecioides. 



If powdered carmine be suspended in the water surrounding 

 a Plumularia, it will, after some little time, be evident that a 



1 " Sur une anomalie chez les Hydromediises et sur leur mode de nutritioa 

 au moyeii de rt'ctoderme," ' Arcli. Zool. Exp.,' viii, 1879 et 1880. 



