( 498 ) 
Considering the ontogenetical processes which contribute to the 
closure of the urogenital canal, as they have been described before, 
I have to join the group of investigators (Rerrerer, ReicHeL, HeRzOG) 
who assume a closure in consequence of the combination of two 
folds (sexual folds) in the median line. I deviate from their opinion 
as to the origin of the sexual folds, which are not the edges of the 
phallus-frame, but which represent folds of the penisectoderm. 
In connection with the processes described above I finally wish to 
give some ideas about the value and the importance of the urethra 
from a comparative ontogenetical point of view. For this purpose 
I have to remind of the state, as it occurs in Echidna, one of the 
Monotremata. In this animal, as Keren’s') investigation taught us, 
a couple of tubes, the so-called “Samenurethra’” and the “Harn- 
urethra’ are developed caudally from the glands of Cowper. The 
former runs like a canal through the penis and is a production of 
the phallus-frame; the latter goes from the urogenital canal oblique 
caudally to the ectodaeum (ectodermal cloaca). Genetically this tube 
is formed, because the original single ectodaeum is divided by 
means of two folds which come together and unite, into two 
halves, the proctodaeum and the “Harnurethra”. For the group 
of the Marsupialia [*) have proved that the urogenital canal must 
not be considered as a homologon to the ‘“Samenurethra” of Echidna 
(as is generally done for the urethra of placental mammals on the 
ground of its topography with respect to the corpus cavernosum), 
but that it must be considered as a combination-product of “Samen- 
urethra” and “Harnurethra’, which placed themselves against each 
other and formed one canal. In Perameles there exists a transition 
between Echidna and placental mammals (man). 
Applying the explanation given for the marsupialia about the 
genetical composition of the urogenital canal to the urethra of man, 
l come to the conclusion that here, too, a real “Samenharnurethra’’ 
exists, homologous to the ‘‘Samenurethra” + “Harnurethra” of Echidna. 
To be compared with the “Samenurethra”’ is that part of the urethra 
which owes its origin to the phallus-frame. The homologa of the 
two folds of the ectodaeum are the two folds which I described as 
sexual folds, by whose meeting the closure of the urogenital canal 
is brought about. The part bounded by these folds thereby becomes 
homologous to the “Harnurethra.” 
1) Keren (F.). Zur Entwickelungsgeschichte des Urogenitalapparates von Echidna 
aculeata var. typica. Semon. zoöl. Forschungsreisen. Lieferung 22. pg. 153—206. 
2) v. p. Broek (A. J. P.) Zur Entwickelungsgeschichte des Urogenitalkanales 
bei Beutlern. Verhandl. der Anat. Gesellschaft. 22. Berlin 1908, pg. 104—120. 
