116 LEECHES 



8-10 days, but then hold them under her body for nearly four 

 months (Mann, 1951). The parent not only provides shelter but 

 by undulating movements of her body provides the young leeches 

 with a fresh supply of water for respiratory purposes. It has often 

 been noticed that young leeches prematurely removed from the 

 parent fail to survive. Since it is unlikely that they had been 

 receiving nutriment it may well be that the ventilatory movements 

 of the parent's body were essential to the young leeches. 



The time when the young leave the shelter of the parent is 

 probably determined mainly by the size of the store of yolk in the 

 crop. When all this has been utilized the young leeches are ready 

 to take their first meal. Pawlowski (1955) records what happened 

 when the young of a Glossiphonia complanata took their first meal. 

 They deserted the parent and attached themselves en masse to the 

 body of a specimen of Erpohdella octoculata. They forced their 

 proboscides as deeply as possible into the body wall of the 

 Erpohdella and proceeded to fill their crops with its red blood. The 

 attacked animal swam, lashed about and almost tied itself in knots 

 in an eff^ort to dislodge the parasites but to no avail. Their 

 posterior suckers were free and their bodies waving freely but they 

 retained their hold by virtue of having their proboscides embedded 

 to the maximum depth. An Erpohdella may survive the attack of a 

 small number of Glossiphonia but the attack of a large number is 

 fatal. 



When the young of Theromyzon tessulatum leave the parent, 

 often on account of the death of the latter, they tend to remain 

 densely aggregated until the opportunity arises to enter the nostril 

 of a water bird. There is at least one case on record (Mann, 1951) of 

 ducklings being killed in considerable numbers by the attacks 

 of young Theromyzon. When dozens of leeches enter the nostril 

 of a bird and there gorge on blood from the mucous membrane of 

 the nose and throat there is danger of asphyxiation or of death 

 from loss of blood. 



4. Development of the Eggs 



The cleavage of leech eggs is basically of the spiral type. Other 

 groups in which this method of cleavage is found include platy- 

 helminths, nemerteans, molluscs other than cephalopods, poly- 



