490 REIGH ARD—PHELPS. [Vor. XIX. 
the sense organs of the tracts. Dean finds further evidence 
for this homology in the structural resemblance of the two 
organs. He says: “As far as histological evidence goes there 
is certainly no difference between the enlarged, thick-walled, 
cup-shaped organs which arise on the snout of the late em- 
bryos of Amia or of Lepidosteus and the typical pit organs 
or sense buds which later occur on other integumental regions. 
It is found, in fact, that a gradation in size exists which con- 
nects the huge sucking organs of the snout with the incon- 
spicuous organs of the trunk.”” In a note he adds: “There 
is but little difference histologically between these (1. €. the 
cup-shaped organs of the adhesive disc) and the neighboring 
nasal pit.” 
Dean’s inference that the existence of pigment across the 
adhesive organ indicates the homology of its constituents with 
the organs of the pigmented lateral line, need not detain us. 
There remains the histological resemblance of the two struc- 
tures which he believes to indicate their homology. 
Such similarity as exists is apparent only and depends 
wholly on the plane of section. Thus certain sections cut 
transversely through the peripheral ends of the cells of the 
adhesive organ cups, resemble sections of the nasal pits lying 
against the adhesive organ and cause the two to be easily 
confused. But when the whole series of sections is examined, 
and sections cut in other planes are compared, the differences 
are much more striking than the similarities. The goblet cells 
of the cups of the adhesive organ can hardly be long mis- 
taken for the cells of pit organs. - The presence of yolk in the 
entoderm cells aids in distinguishing ectodermal and ento- 
dermal tissue in this case as in others. 
All histological differences aside, the development of the 
adhesive organ from entodermal pouches, and its entire dis- 
appearance make it impossible for any genetic connection to 
exist between the adhesive organ and the epidermal sense 
organs in Amia. 
Lepidosteus. Alexander Agassiz (1879) first called atten- 
tion to the adhesive organ in this form and Balfour (1881) 
