114 w - J- CROZIER. 



gland could then result in a condition such as is shown in Fig. 7, 

 the further development of the new glands being prevented. 1 



IV. 



Loeb ('15, 'iSa, 'iS) has sought to account for certain funda- 

 mental characteristics of organ-formation, as seen in Bryophyl- 

 lum, on the basis of a flow of "organ forming" materials. In 

 the case of buds arising from notches in an isolated leaf of this 

 plant, the buds first growing out attract to themselves materials 

 available in the leaf for the growth of buds. The total amount 

 of such materials being limited, the growth of these first buds 

 automatically inhibits the development of others. This explana- 

 tion has the advantageous support of really quantitative experi- 

 ments, and it is of interest to notice how closely it may apply to 

 the not very dissimilar phenomena of gland re-formation on the 

 caudal veil of Chromodoris. 2 



Regeneration experiments have made it probable that the 

 supply of materials to the region of the glands is so slow that 

 over any given period the total available quantity of such material 

 may be regarded as fixed. The relative sizes of the several 

 glands in a set, in cases where size differences are evident, show 

 that a certain proportion of the gland materials is normally re- 

 ceived by each of the (commonly 5) regions of the caudal veil 

 where a gland is characteristically developed. So long as the 

 original glands are present in full activity, no further formation 

 of glands seems to take place. If, however, some of these be re- 

 moved, the current of secretory materials continues to this region 

 of the mantle and results in the formation of an excessive num- 

 ber of new glands, which individually remain of relatively small 

 size. 



1 A distinct tendency is noticeable for the more anterior glands of sym- 

 metrical sets to be smaller than the medial ones, pointing to a bilateral scheme 

 for the distribution of the pro-secretory materials. The exact conditions 

 attending the development of a gland at a particular place can be made clear 

 only from histological study. It seems probable that any portion of the 

 epithelium of the caudal vein can give rise to a gland. 



2 Some perhaps analogous phenomena have been described in the growth of 

 previously injured Madreporarians, where normally there is a " dominant 

 apical zooid " (cf. Wood-Jones, '12, p. 112). The manner in which exhausted 

 gland-cells of the amphibian skin are replaced by the enlargement of previously 

 " dormant " cells is also suggestively similar. 



