INTRACELLULAR DIGESTION OF INVERTEBRATES. 105 



ova in all stages seemed to live much longer when taken from 

 the ovary and placed within the tissues of Phyllirhoe, than 

 when simply placed in sea water. My observations lasted on 

 one individual six days ; that is^ until its death. I was also 

 able to fertilise these eggs within the Phyllirhoe^ normal 

 segmentation and a normal blastosphere being produced. If, 

 however, boiled eggs of Sphoerechinus were introduced, 

 amoeboid cells immediately fastened upon them, and began to 

 devour their yolk. This might be taken as proof that the 

 amoeboid cells eat only dead matter, were it not that in the 

 cases already described, of the ingestion of red blood-cor- 

 puscles, some, at least, must have been alive when they were 

 surrounded or devoured. As a further experiment, I intro- 

 duced a drop of living semen of Sphoerechinus granularis 

 beneath the skin of Phyllirhoe. The spermatozoa slackened 

 their movements, and were soon surrounded and eaten by the 

 mesoderm cells. A few remained for two days undevoured, and 

 retained their power of fertilisation. 



So that the amoeboid cells do not take up everything that is 

 offered them, and we probably should not deny their possession 

 of some means of distinguishing between desirable and unde- 

 sirable substances. But why they made no attempt to attack the 

 living ova in the case described, seems at present inexplicable. 



It has been sufficiently proved, that the cells of the meso- 

 derm have important prophylactic functions ; a result which 

 invites further investigation. Observations on necrotic organs 

 of several Invertebrates, especially of Bipinnaria asteri- 

 gera, have shown it to be one function of the mesoderm cells 

 to devour the dying elements of such organs. The long arms 

 of Bipinnaria end in orange coloured points, covered by an 

 ectodermal pigmented epithelium, and containing more or 

 fewer mesoderm cells. These latter generally contain rounded 

 pigment granules, derived in all probability from the ecto- 

 derm. When the animal has been for some time in a watch- 

 glass, the ends of the arms become worn out and broken, 

 so that large pieces frequently fall off. In the ectoderm of 

 such unhealthy arms are numbers of rounded granules, which 



