31 



of the everted tutule to swell up to the form shown in Pig. 72. 

 Finally the pressure becomes so great that the ring which 

 formed the division "between the inner and outer tuhular cavi- 

 ties (Fig. 61, i.t.c. and o.c.) gives away and a part of the 

 tubule bounding the inner tubular cavity becomes everted. 

 Portions of the central body often adhere to the wall of the 

 tubule and are carried outward and so mark the extent of this 

 second eversion (Fig. 77, g. ) . 



Stage 4« The third eversion of the tubule , accompanied 

 by the inversion of the capsule (Figs. 80 to 82). The in- 

 ternal pressure continues to increase as is shown by the 

 bulging out of the walls of the everted portion (Fips. 78 and 

 79). This brings a strain upon the axis in which the tubule 

 and central body lie. This tends to stretch these structures 

 as is shown by the incurving of the apical wall of the everted 

 portion in Figs. 78 and 79. This causes the base of the evert- 

 ed part to press on the sides of the capsule. This pressure 

 on the sides of the capsule together with an up-pulling along 

 the line of the central body results in turning the capsule 

 through the collar when the last section of the tubule is 

 everted. In Fig. 82 the portions of the everted wall con- 

 tributed by the second, thlrci and fourth stages of the ever- 

 sion are probably Indicated by the granules g^ and g^. Thus 

 we see that the whole transformation may be explained by the 

 increase of pressure in the capsular cavity together with 

 tensions along the line of the inner tubule and the central 

 body*. 



