THE DEVELOPMENT OE EOHINOOARDrUM CORDATUM. 471 
The Development of Echinocardium 
cordatum. 
Part I. — The External Features of the Development. 
By 
E. W. illacBiide, F.R.S., V.P.Z.S., 
Professor of Zoology in the Imperial College of Science and 
Technology. 
With Plates 33 and 34. 
Anyone reading through the comprehensive summaries of 
our knowledge of echinoderm larvae given by Mortensen 
(1898, 1901) must be struck on the one hand by the large 
number of varieties of echinoderm larvm described therein, 
and on the other hand, by the paucity of cases in which the 
parentage of the larva had been accurately determined. 
In the summer of 1911, when working at the laboratory 
of the West of Scotland Marine Biological Association, situated 
at Millport on the Isle of Cumbrae on the Firth of Clyde, I 
succeeded in artificially fertilising the eggs of Echino- 
cardium cordatum, and in rearing the resulting larvae 
through the whole period of their free-swimming life until 
they metamorphosed into young urchins. Last summer, 
(1913) I returned to Millport and repeated my experiments, 
and again succeeded in rearing the larvas of this species 
through their entire development until the completion of meta- 
morphosis. Drawings of the larvae at every stage of their 
development were made from living specimens, and thes:> 
drawings, slightly corrected by comparison with larvae 
preserved and mounted whole, have been used to illustrate 
this paper. 
I had originally intended to delaiy publication until I should 
have had leisure to work out tlie internal features of develop- 
VOL. 59, PART 4. NEW SERIKS. 31 
