at tiner. , yet this Siffero^ce is not const-rit and th'-y ?.ll 

 ho.ve. the zc.^e valu^ in develoT-enlj; that is, thoy are -not 

 divided in to macromeres and -nicroTeres, As** There is no 

 evidence either fro"^ observations of the livin,!7 egc^s, or 

 fro- the ntudy of sections of rreservpd Tiaterial that any 

 of :he blastomeres can be localised as forninp distinct 

 oarts of the future errbryo. During the first t-70 or three 

 cleavages the -rocess is usually cui$c regular , but beyond 

 the '"Ight cell stage the segnentatio^^ berores very irregular 

 and erratic; almost if not fully as ren^arhable as that de- 

 scribed and figured by Harritt for Pen]2?'li§ M^rlPlli^ and 

 of ;;hich he says; "Between the rxtremes of the en^bryoric 

 history fro"- the early cleavage to the forration of the 

 -orula are to be found the '^ost erratic and ancalous exhi- 

 bitions of develo- mental nhenoTe-a v;hioh have ever cone to 

 Tiy knovrledgo, if indeed its countermart has hitherto -"been 

 known. It is not strange that v;ith the -ic-tal Tnctures of 

 such sfady-going exhibitions as are found in the develon- 

 ment of annelids, -.olluscs, etc., one should regard such 



