1920.] Cocoon-formation by the common Lahore Leech. 343 
On May 30 one freshly laid cocoon was found in each of the 
pots containing leeches Nos. 1 and 14. The immediate cause 
of this appears to be the scarcity of moisture since these pots 
were nearly dry when they were examined. Similarly on June 
4, a freshly laid cocoon was found in the pot containing leech 
No. 15, which when examined was found to be almost dry since 
no water was poured into the pot or dish on the previous day. 
On June 6, cocoons were found for the first time in the pots con- 
taining leeches Nos. 13, 23, 24, 30 and 31 and a second cocoon 
in No. 19. The pots containing these leeches were emptied of 
water on the previous day. 
t would appear from these observations that cocoon-lay- 
ing is induced by tendency to dryness and rise of temperature, 
i.e., by adverse conditions. This suggestion is supported by 
the behaviour of the control-specimens. A fresh supply of 
the remaining one in an earthen pot (No. 1) with two lumps of 
moist earth and sufficient water to keep the lumps submerged. 
The water in both the jar and the pot was renewed every day. 
On June 5 one of the specimens from the glass jar was put 
into an earthen pot (No. 2) in water but without any earth 
inside, the pot being placed in an earthen bowl of water. 
None of these control specimens lay cocoons, although those in 
the glass jar were kept alive till the end of August. 
The contents of the cocoon form a dark-grey jelly. Dev- 
elopmeat takes place when cocoons are kept on damp earth, but 
they should not lie immersed in water nor should the cocoons 
be covered over with mud. Young ones hatch out in about a 
fortnight through an opening on one end of the cocoon. It is 
possible that in summer development may be accelerated by 
the heat. From a cocoon three or four to fourteen young ones 
hatch out varying in size to a slight extent. They are about 
20 mm. long and 3 mm. broad, when extended about 25. mm. 
sucker. These have the general shape of the adult leech but 
ing visible through the more or less transparent skin. In a few 
ays the characteristic colour-pattern appears. Two broods— 
kept alive in water from June to the end of August. The dark- 
grey contents of the cocoons are almost completely used up 
when the young ones are hatched out. ; 
The large size, spongy outer layer and dark-grey contents 
distinguish the cocoon of the leech from that of the earth- 
worm. 
