6 
NATURE NOTES 
one was seen to take any part in the work. In a case in which 
a female was observed to oviposit in a nest already containing 
eggs, the male immediately bound with threads the part of the 
nest in which the new cluster had been placed. 
Details of much interest are given by Mobius respecting the 
source and nature of the threads ; and his findings have been 
confirmed by Prince. M("*bius, it is said, has shown that “the 
kidney of the fifteen spined stickleback acts asa spinneret ”®; and 
it is true that the secretion of which the thread is composed was 
ascertained by this naturalist to originate in the kidneys. He 
found further that the secretion is stored in the urinary bladder, 
and is emitted, in a thread-forming condition, from the urinary 
aperture, just behind the genital pore and anus. The author 
stated that the thread is usually o-i2 — 0'i3 mm. in diameter, 
and that the microscope shows it to consist of several cords 
stuck together, which in their turn are composed of very fine 
parallel filaments. The substance is nitrogenous, and is a 
peculiar modification of mucin. The matter is formed, in the 
kidneys, by the epithelial cells of the urinary tubules, which 
exert this form of activity only during the breeding season ; at 
this time the kidneys are much inflated, and from them the 
mucus passes through the ureters into the urinary bladder (now 
dilated into a large pyriform vesicle), from the opening of which 
— the urinary aperture — the mucus finally oozes and adheres 
to foreign bodies. After the breeding season the volume of the 
kidneys and bladder diminishes, and these structures then con- 
tain urine only. Prince also found the male’s kidneys consider- 
ably swollen at breeding time; and sections revealed an altered 
condition in the urinary tubules, the epithelial cells of which 
were evidently active in the secretion of thread-forming mucus ; 
the ureters were of great capacity ; and the urinary bladder, 
acting as a reservoir for the mucus, was much distended. The 
matter assumes a fibrillar character while yet in the ureters and 
bladder. Its flow from the urinary aperture is doubtless under 
the control of the animal ; but it is very abundant and often 
appears to ooze involuntarily. When a mass of sea-weeds has 
been selected for the nest, this author says, “the fish has merely 
to approach closely, so that the protruding mucus may adhere 
to a projecting frond, and by passing and re-passing round the 
mass the weaving operation is accomplished. Occasionally a 
rapid ejaculatory movement is observed, and it is interesting 
to note that the threads are not carelessly superposed, except 
when necessary for increasing the density of the nest, but are 
crossed at an angle by the varying movements of the fish, so 
that rhomboidal spaces are enclosed and a regular reticulum 
is thus produced.” The several strands composing the thread 
measure, according to this author, -oooS — -00092 of an inch in 
diameter, the complete thread having a diameter of -0046 — 
Houlen(;er, “ Zoolo(;ical Kccoid,” xxiii. (1886) ; “ Pisces,” ]i. 16. 
