42 LEECHES 



2. In Rhynchobdellae 



Our knowledge of the nutrition of rhynchobdellid leeches is 

 very scanty indeed. Food is obtained by inserting a proboscis into 

 the tissues of the host. Many are fish parasites, but it is somewhat 

 surprising that a proboscis containing no hard skeletal parts can 

 be forced through the integument of a fish. A study of the forces 

 involved would prove interesting. Many rhynchobdellids have 

 a pair of diverticula between the base of the proboscis and the 

 beginning of the crop. In Placohdella costata according to 

 Reichenow (1922) the walls of the diverticula are made up of two 

 kinds of cells, tall columnar cells and broad ones. The latter con- 

 tain numerous thread-like micro-organisms and these organisms 

 are also found in the posterior part of the crop. This leech sucks 

 tortoise blood and in the neighbourhood of the micro-organisms 

 the blood corpuscles were haemolysed, while elsewhere they were 

 not. This might well be a case of digestion by symbiotic micro- 

 organisms. On the other hand, Reichenow also suggested that 

 symbiotic micro-organisms were responsible for digestion of 

 blood in certain mites and insects. These were subsequently 

 shown to have adequate gut enzymes and Wigglesworth (1953) 

 suggested that the micro-organisms supply vitamins or other 

 essential growth factors. 



Jashke (1933) examined the oesophageal diverticula of various 

 other rhynchobdellids including Piscicola geometra, Cystohranchus 

 respirans and Branchellion torpedinis. He found that these diverti- 

 cula never contained blood but were filled instead with an 

 albuminous fluid in which were suspended large numbers of 

 bacteria. Once again these might well be micro-organisms respon- 

 sible for the digestion of blood, but their presence in the crop has 

 not so far been detected. A systematic survey of the crop flora of 

 leeches is much needed. 



The food reserve of the rhynchobdellid leech Glossiphonia 

 complafiata appears to be mainly in the form of fat droplets. 

 Adipose cells are a very prominent feature of the connective tissue 

 and Bradbury (1956) has shown that ten weeks' starvation results 

 in a 95% reduction in the volume of the contained droplets. 

 Putter (1908) found that fat metabolism is comparatively 



