46 HARLEY N. GOULD 



take on the same structure which is being assumed by the ovi- 

 duct at the same time; i.e., the walls, originally of thin flat cells 

 like the pericardium, begin to form a cubical epithelium which 

 acquires cilia and becomes thrown into longitudinal folds. 

 Eventually it possesses unicellular glands of the same nature as 

 those in the oviduct. It is of interest that the differentiation 

 of the gonopericardial duct proceeds from the distal end, at its 

 junction with the oviduct, and toward the pericardium. At a 

 certain stage the distal part is composed of cubical ciliated epi- 

 thelium, with ridges reaching into the lumen; the middle part 

 has a thinner wall, but cells are dividing to form outgrowths 

 into the lumen; in the proximal part (nearest the pericardium) 

 the wall is composed of thin flat cells like the pericardium. In 

 the adult stage the folded, glandular, cubical, ciliated epithe- 

 lium extends the full length of the gonopericardial duct, and 

 even projects somewhat into the pericardium. 



Whatever the phylogenetic significance of this organ (Giese, 

 '15) may be, one cannot escape the conviction that so highly 

 differentiated a structure, occurring only in the female phase, 

 must have a functional value connected v/ith reprodujction. 

 The walls are so folded that they are capable of expansioii like 

 those of the oviduct, as though for the purpose of allowing eggs 

 to enter; yet it is not clear what advantage could accrue from 

 passing the eggs toward the pericardium before their entrance 

 into the uterus, unless there is some action of the Ijanph in the 

 pericardial chamber upon the ova. In this connection it will 

 be recalled that the body fluids of animals so far as known 

 inhibit, rather than facilitate, the fertilization of eggs by sperm 

 (Lillie, '14). 



GENERAL CONSIDERATIONS: ORIGIN OF GERM CELLS IN 

 HERMAPHRODITE MOLLUSCS 



In conclusion, it will be in place to consider what application 

 can be made, from the obseivations, to the question of the 

 origin of germ cells in hermaphrodites. The volume of work 

 on this subject is very small and the conclusions of the various 

 workers do not agree, even on the same material. The studies of 



