4.96 M. D. HILL. 
also in Arthropods! has this phenomena been observed. 
Hargitt cites many instances, and by his own work adds one 
more, for the case of Pennaria is in many ways strikingly 
like that of Aleyonium. He is at least convinced that an 
enucleate stage is always to be found in the early development 
of the egg of Pennaria. I shall again refer to Hargitt’s paper 
in dealing with the phenomenon of fertilisation. 
METHOD. 
Stocks of Aleyonium digitatum were kept in tanks in 
the laboratory, and their ova fertilised, preserved, and cut 
into sections according to the usual methods. Various pre- 
serving fluids were tried; the best results I obtained by 
leaving the eggs for twenty minutes in a saturated solution 
of corrosive sublimate with a few drops of glacial acetic. 
With Fleming’s and Perenyi’s fluids I had less good results, 
especially with the latter fluid, so often recommended for 
eggs which contain a good deal of food-yolk. ‘The extreme 
opacity of the eggs quite prevents any glimpse of the process 
of maturation and fertilisation going on in the living egg. 
In fact, for cytological studies the egg of Aleyonium proved 
a most unfavourable object. Partly owing to the difficulties 
described above I was unable to make accurate observations 
of the actual time that elapsed after the eggs and sperms 
were mixed before segmentation took place. I therefore 
was obliged to preserve batches (about 30) of ova at short 
intervals. In consequence, much material accumulated, of 
which by far the greater part had to be discarded, for, as the 
non-segmentation of the ova showed, no fertilisation had 
taken place. 
MATURATION. 
Maturation usually occurs before the egg leaves the polyp, 
and the ova when expelled are ready for fertilisation. Never- 
theless, if an egg be taken from the parent colony it will 
mature while floating in the water. The egg on emerging 
1 « Zur Entwick. der Dekapoden,” ‘ Jenaische Zeitschrift,’ xi.’ 
