LIFE-HISTORY OF XENOPUS LAVIS, DAUD. 809 
gland lies, swings out away from the membrane and never touches it. There 
was not the slightest bulging of the membrane opposite the head in the reversed 
eggs.™ 
Regarding the action of the secretion of the frontal gland, there seems to be 
reason to believe that it is digestive, and probably is due to a peptic ferment. 
Miss R. Atcock (’91 and ’99) discovered that the external epithelium of the skin 
in the Ammocetes of Petromyzon planert and in P. fluviatilis produces a peptic 
ferment capable of digesting fibrin in a 02 per cent HCl solution. In the 
frontal gland, then, a similar secretion is probably localised in an appropriately- 
placed patch of epithelium, and the acid medium requisite for the action of the 
peptic ferment is, no doubt, supplied by the excretion from the pronephros. But 
it is not necessary to dwell on this poimt, as the specific action of the frontal gland 
ean no doubt be tested by experiment. 
It is obvious that the frontal gland is actively secreting at hatching time 
from the coating of secretion which hardens on the surface of the gland in larve 
preserved at this stage. The light band seen (fig. 15) running along the middle 
of the gland is produced by coagulated secretion. After hatching, the frontal 
gland begins to atrophy, and has disappeared three or four days later, before the 
tadpole begins to feed. 
Considerable morphological importance has been attached to the frontal gland by 
von Kuprrer (’93, p. 78, 94 and ’03, pp. 188 and 190). He regarded it as the 
“anpaarige Riechplakode” of the frog and uses it as evidence of a monorhine stage in 
the development of an amphirhine form of Vertebrate, believing that it arises as a 
sensory thickening of the ectoderm at the spot (the neuropore) where the brain retains 
its connection with the ectoderm longest; the connection he considered to be the 
primitive unpaired olfactory nerve. It would not be necessary to refer to this view 
here if von Kuprrer had not repeated his interpretation of the ‘‘ Stirnknospe” in his 
chapter on ‘‘ Die Morphogenie des Centralnerven-systems” in O. Hertwie’s “ Hand- 
buch der Entwicklungslehre der Wirbeltiere.” In the same work Karu Prrer (’02), in 
the chapter on ‘“‘Die Entwicklung des Geruchsorgans in der Reihe der Wirbeltiere,” 
gives weighty reasons for rejecting von Kuprrer’s fascinating theory of Mono- and 
Amphirhiny (Prerer, ’02, pp. 12-13, p. 26). Prrsr, in this chapter, refers to his own 
paper on voN Kuprrer’s theory (01, p. 654), where he includes observations on Bufo 
“emerea” (syn. B. vulgaris), showing that the ‘‘Stirnknospe” has in the toad no 
connection with the neuropore and that it must be placed in a different category to the 
sense-organs Of the Anura, since it develops from the external layer of the ectoderm, 
while the sense-organs are all derived from the inner nervous layer (see also PeTErR, 01a). 
CoRNING (’99) and Hinspere (01) have described the frontal gland in Rana temporaria 
and f. esculenta, and it can be gathered from their descriptions and Prrer’s of the 
3 
* It has been possible to show by experiment on Hyla larve that the surface of the frontal gland only, and no ~ 
other part of the ectoderm, has the power when touching it to soften the vitelline membrane.—9th April 1904. 
