STRUCTIIKE OF THK EXCRETORY OR(4AN.S OF A.MPHIOXrS. 195 
the cocloinic epithelium, allowing the fluid to bathe the tubes. 
Nevertheless the whole excretory organ is to be considered 
as retroperitoneal. 
Part 3. — The Nephridium of Hatschek. 
'I’his organ was first described by Hatschek in a paper 
without illustrations (9), wherein he states that the first 
somite of the left side divides into two halves, of which the 
first acquires an opening to the exterior, and becomes the 
“ Riiderorgan” or ciliated glandular joit in the buccal cavity, 
while the second and inner half becomes the nephridium. 
“ Es entwickelt sich in der Larve als rnesodermaler wim- 
pernder Trichter und canal, und zwar nnr linkerzeits vor der 
Munddffnung, in der Region des ersten Metamers ; es wiichst 
spilter weiter nach hinten aus. Bei dem ansgebildeten Thiere 
erstreckt sich das Organ an der linken kdrperseite lungs des 
ventralen Randes der Chorda von nahe dem vorderen Mun- 
drande bis dicht hinter das Velum. Hier scheiut es in den 
Kiemendarm zu rniinden (die Ausmiindung muss ich noch- 
mals priifen). Es liegt in einem engen Fortsatz der Leibe.s- 
holile iiberlagert von der linken Carotis ” (9). 
Lankester and Willey incidentally refer to the organ in 
their important memoir on the larva of Amphioxus (10), and 
there state that “ in the condition in which we have observed 
this structure (viz. in larvic ranging from the stage with 
three gill-slits up to closure of the atrial cavity) there does 
not seem to be any special reason for regarding it as a 
nephridium. We should prefer to call it the subchordal 
tube. It appears to end blindly anteriorly, and to open into 
the buccal cavity near the recurved extremity of the gland- 
ular tract which accompanies the club-shaped gland.” 
Willey in his later contribution (15) incompletely repre- 
sents the nephridium of Hatschek in his figures, but actually 
draws the solenocytes without, hoAvever, realising their 
significance. He says, “1 could not certainly detect cilia in 
it, and, in fact, was unable to understand its import. It 
seems to possess a superficial resemblance to the head-kidney 
