61 



to regard it (at least in X. fimbriata) as defucnerate. 

 Likevfise, I am inclined to repjard the rormation of the 

 spherical cells, in the one part, as not the ctiief func- 

 tion of this part of the ^land. The origin and fate of 

 the cells I have not been able to determine. Their con- 

 tents suggest that they may be modified mucous gland 

 cells. 



V/hat the special function of this remarkable struc- 

 ture is I am not able to even guess. The rudimentary 

 character of the anterior part in the "head" of T. nava- 

 lis indicates that it cannot be the formation of a secre- 

 tion to soften v/ood. Its development in the gill, in 

 small as v;ell as large individuals, in male and female, 

 and in forms that do not retain the eggs in the gills, 

 proves that this part caiinot be for the nutrition of viv- 

 iparous embryos. The close connection with the gill indi- 

 cates , it seems to me , that its function is probably the 

 elaboration of some internal secretion for whose formation 

 the presence of both blood and water is necessary. 



