TISSUE DIFFERENTIATION AND RATE OF GROWTH. 195 



less fortuitous!} 7 coincident with the general maximum. Coin- 

 cidence of this sort is hardly to le expected in all annelid-. Tin- 

 abrupt rise for the tenth regenerated Moment after the twelfth 



r 



day i- e\ idently due to accidental conditions in the gn >u: 



For the differentiation study, longitudinal -ection- were u-ed 

 almo-t e\clu-ivcly. All of these were sagittal or nearly so. 

 While cro-- -ection- would certainly have given lie tier hi-tological 

 detail they would have made it very difficult to interpret con- 

 dition-in gnu-nt-. The number of specimens favor- 

 able lor sectioning wa- too -mall to allow tin- u-e of l>oth kinds. 

 'I'lie general feature- of the rate of d i ffen n t iat ion in the rcgenerat- 

 iiu* p.trt ma\ In- readih -r.i-ped l'\ reference to Table III. The 

 ' rookedni ome \ the \\orm- and the -mall -i/e of all made 

 interpretation ol the -ection- rather difticull -ince -o fe\\ -ections 

 ill each -pci iinen could : a approximately radial. Then' 

 ua- the turiher dil'licnli \ . \\ith many, of the tine -and in the 



ii.hiiu and clouding the -ection even when 



it did not tear it. In -pile of the-e di-ad\ am ao - the character- 

 IStics "I mo-t ti--ue- -ho\\ed preit\ \\ell their relation- to the 

 einliiAonic and mature < < mdit i >n-. Ten ti ue- and oi-^an- are 

 laiih ea-il\ di-tin^iii-lu-il in the mid Ixxly region of the normal 

 \\oiin. Iht '-e \\ill no\\ In- o.n-idered -eriatim. 



Matnie cpidrrmi- i- one la\er in thickiie-- \\ith the form of 



cell \ a i A iir^ 1 1 < -m tlat to Cuboidal acci ndiir^ to -late ( >\ e\teii-i< .n 



li-j. 5 . There i- a \\ ell-<|e\ el. i| H d (iitiile. In regeneration 



there i- tir-t an extreme extension ot ( pidennal cell- in the neiiji- 



I" 'i hood of the injniA \\ 1 lit-li in a !e\\ houi - results in a covering 



-I the i nt surface. Thi- e\ ten -ion i- carried SO far that the eel 1- 

 aie ijuile thin and aln io- 1 -epa rated Irom each other. Then tollou - 

 .t period of M-IA rapil proliferation in which the cell- are three 

 or four deep I ig. l These cell- are qui'e -mall, rounded. 

 irregularU arranged and I!HA ha\e very little c\to|>la-m. Thi- 

 coiidition .madualK changes until a portion lour days old -Imu- 

 onl\ a -iir^le !a\ e< . The cell- IA en then are \\ ithollt \\ell-marked 

 \\all-. their nucU-i are -till prominent and thev lack the ilelinite- 

 ness SO characteri-'ic of the mature epidermal cell. A cuticle i- 

 ea-il\' di-tin-ui-hed 1>\- the tilth ila\ and a -ixth da\ <-pidermi- 

 --entially mature though still -taining a little differently and 



