TIIM DKVELOPMI^NT OF Fi^HlNOCARDI UM CORDATF^F. 473 
I am also especially indebted to Dr. Gemmill, Lecturer in 
Embryology in tlie University of Glasgow and Vice-President 
of the West ot‘ Scotland Marine Biological Association, for 
the pure cultures of the diatom Nitschia with which lie 
supplied me both in 1911 and in 1913. To these cultures I 
ascribe my success in rearing the larvae through the whole of 
their development until the completion of metamorphosis. 
The methods adopted were exceedingly simple. The 
laboratory at Millport is situated close to the fairway of the 
Firth of Clyde, and the water which streams up the firth with 
every incoming tide is quite uncontaminated and perfectly 
suitable for rearing the larvae; the only precaution which it 
is necessary to observe is to procure the water a few yards 
from shore and to convey it to the laboratory in an earthen- 
ware or glas^ vessel, since sea- water rapidly contracts 
contamination from metallic vessels, and for this reason the 
sea-water which is pumped into the tanks at Millport is 
unsuitable, since it passes through metallic pipes before 
reaching the laboratory. 
The entire development up to the completion of metamor- 
phosis occupies a period of about four weeks, aud is, therefore, 
very rapid as compared with the development of Echinus 
esculent us, for in this latter species at least six weeks 
must elapse before the metamorphosis is completed, and under 
laboratory conditions a period of two months and more is not 
infrequently required before the imago condition is attained. 
A brief resume of the times (reckoned from the moment of 
fertilisation of the egg) required for the attainineut of well- 
marked stages in the developmental history of Echino- 
cardium cor datum is given below : 
Free-swimming blastula . . . fO hours 
Formation of primary mesenchyme and 
incipient gastrulation . . . .15 
Gastrulation completed . . . . 30 ,, 
Formation of coelom and first trace of 
stomodaeum, the post-oral (anal) arms 
of the larva formed .... 
2 days 
