462 W. DE MORGAN AND THE LATE G. HAROLD DREW, 



13tli. The edges have curled over more, and ten knobs on them are 

 more accentuated. The centre plate thinner, and at points clear spaces 

 appear. 



15th. Cut off the end of the vertical projection. 



16th. Perisarc had reformed round the cut end and the incised 

 piece. 



SUMMARY AND CONCLUSION. 



1. The Hydroids experimented on were Antennularia ratnosa, and A. 



antennina. 



2. These were cut in pieces and pressed through bolting silk, with the 



result that isolated cells and small cell aggregates were obtained, 

 which soon aggregated together to form compact masses. 



3. These restitution masses secreted a perisarc within from 12 to 18 



hours. 



4. Various changes in shape, and general retraction of the mass away 



from the perisarc occurred later, but even up to 60 days there was 

 no sign of the regeneration of the hydranths. 



5. The restitution masses consisted of ectoderm and endoderm cells, 



and in addition such structures as nematocysts, ova, and broken 

 down cells, all of which were subsequently absorbed and played no 

 part in the future development. The ectoderm cells were relatively 

 little damaged, and were embedded in a plasmodial mass formed 

 by the endoderm cells. 



6. A definite layer of ectoderm cells is formed on the surface, and these 



cells secrete the perisarc. 



7. Gradual aggregation and segregation of the endoderm cells from the 



plasmodial mass takes place ; and they form very definite tubules 

 similar in structure to the ccenosarcal tubules continuous with the 

 enteric cavities of the normal hydranths. These tubules are em- 

 bedded in a mass of ectoderm cells, they are convoluted and ramify 

 in all directions. Many granules develop in the cytoplasm of these 

 cells, and after about a month many of them have degenerated. 



8. The ectodermal cells show no signs of degeneration, and the masses 



containing them have been kept alive for 60 days at the time of 

 writing. 



9. In none of the experiments was there any sign of the occurrence of 



cell division. 



