4.94, M. D. HILL. 
1895 he suggested that I should take the matter up. He 
most kindly handed over to me all his material, preparations, 
and the notes he had made thereon. I found, however, that 
certain important stages were missing, and if the work was 
to be completed, it would be necessary to obtain ova pre- 
served after artificial fertilisation, in all stages up to the 
time of the beginning of segmentation. ‘To gain this object 
proved far more difficult than either of us had imagined, 
and altogether we made five attempts to obtain ova in the 
right stages of development. I myself visited Plymouth in 
December, 1896, and January, 1897, and at the same season 
in 1902-3. In 1900-1 I sent my laboratory assistant. 
It was, however, only in the first week of January, 1903, 
that I was able to get anything approaching to satisfactory 
material, and I am much indebted to Dr. H. J. Allen, Director 
of the Plymouth Biological Station, for the zeal with which 
he did all that was possible to provide me with ripe colonies 
of Aleyonium. 
Aleyonium digitatum breeds at Plymouth during the: 
coldest and stormiest part of the year, from the middle of 
December to the middle of January. Colonies in sufficient 
numbers could only be caught in the nets of trawlers, and 
owing to storms and Christmas festivities I had to wait many 
days before material could be procured. 
But even with the Plymouth tanks full of Aleyonium 
digitatum, the difficulties of the investigation had but 
begun. In 1896, for instance, I found that in a hundred- 
weight of Alcyonium there was only one male colony with 
free spermatozoa, and that was discovered the day before I 
had to leave. Furthermore, the spermatozoa were but faintly 
mobile, so that the investigation had to be abandoned for 
that year. In 1902-3 I was more lucky, and was able to make 
several partially successful fertilisations. But at the best not 
more than 10 per cent. of the ova gave satisfactory results. 
It is often very hard to tell whether eggs have really been 
fertilised until they are cut into sections, as in the early 
stages the blastomeres are vaguely defined, and hardly, if 
