TWO ABNORMAL PLUTEI OF ECHINUS. 
249 
to it, builds up an individual. We can only remark that if 
this be the case our second larva is an instance where the 
entelechy lias been deceived, and has been led to construct a 
creature which could not possibly have survived. 
Millport, Scotland, 
July 17th, 1911. 
List of Works Heferred to. 
1. Allen, E. J., and Nelson, E. W. — “ On the Artificial Culture of 
Marine Plankton Organisms,” 6 Journ. Mar. Biol. Assoc.,’ vol. viii, 
No. 5, p. 65, 1910. 
2. Bather. — * Text-book of Zoology,’ edited by Sir E. R. Lankester, 
vol. iii, “ Echinoderma.” 
3. Driesch, H. — “ The Science and Philosophy of the Organism,” 
' Gifford Lectures,’ 1909. 
4. MacBride, E. W. — “The Development of Asterina gibbosa,” 
‘ Quart. Journ. Micr. Sci.,’ vol. 38, 1896. 
5. “The Development of Echinus esculentus, together 
with some Points in the Development of E. miliar is and E. 
acutus,” ‘Phil. Trans. Roy. Soc.’ (London), Series b, vol. cxcv, 
1903. 
6. “The Development of Ophiothrix fragilis,” ‘Quart. 
Journ. Micr. Sci.,’ vol. 19, 1906. 
EXPLANATION OF PLATE 24, 
Illustrating Prof. E. W. MacBride’s paper on <f Two Abnormal 
Plutei of Echinus.” 
Key-list of Abbreviations used in Illustration of the 
Figures. 
Ad. Adoral band of cilia. a.l. Antero-lateral ciliated arm. am. 
Amniotic cavity, am} Amniotic cavity abnormally developed on the 
light side of the larva, calc. Calcigenous cells in the interior of the 
adult spines. d.ep. Dorsal ciliated epaulette. ech. “ Echinus-rudi- 
ment” on the left side of the larva. ech } “ Echinus - rudiment ” 
abnormally developed on the right side of the larva. l.a.c. Left 
anterior coelom of the larva, l.hy. Left hydroccele. m. Adult mouth. 
mp. Madreporic pore. nerv. Adult nerve-ring. p.d. Postero-dorsal 
ciliated arm. ped. Median dorsal pedicellaria. ped } Lateral pedi- 
