PRELIMINARY ACCOUNT OF DEVELOPMENT OF LAMPREYS. 153 
day of embryonic life; it soon shows a lumen, and anteriorly 
opens into the pleuro-peritoneal cavity. At the anterior end of 
this duct are formed a series of ciliated tubes opening by wide 
funnel mouths into the body-tavity, and on the other side 
by narrow tubes into the duct. A glomerulus is then formed on 
each side of the mesentery, just as in the Amphibia, and the 
whole organ thus developed is the head kidney (Miiller’s Vor- 
niere). Although I cannot prove it with absolute certainty, it 
is yet in the highest degree probable that the ciliated tubules 
are a development of the duct itself. The duct empties into the 
now empty hind gut even in the embryos. It is to be especi- 
ally noted that the head kidneys form for quite along period the 
only excretory apparatus of the larva, the first rudiments of the 
Wolffian bodies not appearing until the larve have reached a 
length of 9 mm. These rudiments are metameric involutions of 
the peritoneal epithelium, at first solid, which soon become 
hollow and open into the body cavity and the segmental duct ; 
they differ from those of the Elasmobranchs in being lateral to 
the ducts. As Miiller has shown, the head kidneys gradually 
become atrophied and disappear. 
The segmental ducts at first open separately into the hind gut 
near the anus; shortly before the metamorphosis they come 
close together and form a common canal. The anal opening 
becomes longer, and finally a part of the hind gut becomes con- 
stricted off and forms the sinus wrino-genitalis, and receives a 
separate external opening. The wall of the sinus is perforated 
at two points to form the abdominal pores. 
My investigations upon the genital organs are yet far from 
complete. As far as they have yet gone, they agree with the 
results of Miiller. : 
Princeton, Vovember 29th, 1880. 
