264 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



Ripe ova of Arenicola clajJciredii 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 coelomic 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)f and a 

 smaller (A. B), each of which in less than an hour divided 

 again. +. Three of the cells (A 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, lb, 1c, Id) 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 Polychseta. These four upper cells form 

 the first quartette of ectomeres. From the four lower 

 cells (1A, IB, 1C, ID) a second (fig. 72) and a third set 

 of four (2a, 2b, 2c, 2d, and 3a, 3b, 3c, 3d) are successively 



development given in the following account were made on various 

 batches of eggs and larvse and extended from this date until May 19th, 

 when the last of the larvse 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. 



t 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. 



I 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 fur 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. 



