184 
Ripe ova of Arenicola claparedii were artificially 
fertilised by adding to the sea-water in which they were 
contained a small quantity of sea-water containing 
spermatozoa taken from the caelomic fluid of a mature 
male. In one to two hours after this the two polar 
bodies were extruded, and in about four hours after the 
addition of the spermatozoa nearly all the eggs had 
divided into two cells (fig. 69), a larger (C D)T and a 
smaller (4 B), each of which in less than an hour divided 
again.t. Three of the cells (4 B C) so produced were 
nearly equal in size; the fourth (D) was considerably 
larger than these (fig. 70). By the next division each 
cell was cut into an upper or anterior and a lower or 
posterior portion. The four upper cells (la, 1b, le, 1d) so 
produced become displaced, or rotated, with respect to the 
axis of the:egg, so that each no longer lies directly above 
the cell from which it arose (fig. 71). This rotation, 
which affects nearly all the cleavages of the first day, is 
characteristic of the “ spiral ’ type of cleavage found in 
Nereis, and other Polycheta. These four upper cells form 
the first quartette of ectomeres. From the four lower 
cells (14, 1B, 1C, 1D) a second (fig. 72) and a third set 
of four (2a, 2b, 2¢, 2d, and 3a, 3b, 3c, dd) are successively 
development given in the following account were made on various 
batches of eggs and larvee and extended from this date until May 19th, 
when the last of the larvie died. I beg to express my sincere thanks 
to Professor Dohrn for his generosity in placing a Table and the 
resources of his Station at my disposal, and to the Government Grant 
Committee of the Royal Society for a grant towards the expenses 
of this and other work done in Naples. 
+ I have used Dr. Child’s nomenclature of the cells, which is based 
on that proposed by Wilson in his classical memoir on ‘‘ The Cell 
Lineage of Nereis,’’ Journal of Morphology, Vol. VI. 
t The early development of A. claparedii appears to be very 
similar to that of A. cristata, which has been studied in great detail 
by Dr. C. M. Child (see Archiv fiir Entwickelungs-mechanik der 
Organismen, Band IX., Heft 4, May 22nd, 1900). See also 
E. B. Wilson, Studies from the Biological Laboratory, Johns Hopkins 
University, Baltimore, Vol. II., 1883, pp. 271-299. 
