480 HIROSHI OHSHIMA 
it seems not unnecessary to put on record detailed descriptions 
of the skeletal structure of the larva of Spatangus pur- 
pureus. 
The material on which my work is based consists of a series 
of larvae, reared and preserved by Mr. Elmhirst at 
Millport, and kindly handed over to me for study by Professor 
HE. W. MacBride.? Although there are found several gaps 
in developmental stages, the changes undergone by the larval 
skeleton could be followed fairly satisfactorily. From the 
labels which were found attached to the vials we obtain the 
following chronological accounts. 
The earliest stage which is represented by segmenting eggs 
is dated 16th May 1914. This is probably the day on which 
the eggs were artificially fertilized. The further stages with 
regard to the age in days are : 
2nd day May 17th . SDlastula. 
BEIT; ene Sth tie ss . Gastrula. 
Mi: & sh Ath : . Young 2-armed pluteus. 
bth 55 ,» 20th . Fully-formed  2-armed 
pluteus. 
6th 5 se  Dilist , . 4-armed pluteus. 
ithe, June Ist . ; . 6-armed pluteus. 
2 ? : : . §8- or 10-armed pluteus. 
24th ,, June Sth : . 12-armed pluteus. 
Thus in full accordance with the statements of Mortensen 
(6, p. 15) the larva reaches its last stage in the course of 
three weeks. It is to be regretted that those larvae whose 
skeleton was best preserved had been kept together in one 
vial, all the different stages being mixed up, and without any 
label, so that it is not possible to give a chronological state- 
! The present work was done partly in the zoological laboratory of the 
Imperial College of Science and Technology and partly in the British 
Museum (Natural History). My cordial thanks are due to Professor 
E. W. Mac Bride of the College and to Sir Sidney F. Harmer of 
the Museum, for help and encouragement in various ways and for the 
privilege of the use of the laboratory and the libraries. 
