iv. 6 



FEEDING OF LAMPREYS 



groups of muscles that rock the tongue up and down to produce a 

 rasping action. The muscles of the sucker are all derived from the 

 lateral plate and are innervated from the trigeminal nerve; their fibres 

 are striated. 



The mouth is a small opening above the tongue and leads into a 

 large buccal cavity. At the hind end this divides into a dorsal passage, 

 the oesophagus, for the food, and a ventral respiratory tube, which 

 leads to the gill pouches but is closed behind. At the mouth of the 



ann. 



m. card.ap. 



circ.m. 



mus.2 mus.t 



Fig. 54. Longitudinal section through head of lamprey. 



ann. annular muscle of sucker; b. brain; circ.m. circular fibres of tongue-muscles; oes. oeso- 

 phagus; g. gill aperture; h.s. hypophysial sac; m.card.ap. cardio-apical muscle; mus. 1 and 

 2, muscles that rock the tongue; n. notochord; nas. nasal sac; nos. nostril; p. pineal; pit. 

 pituitary gland; t. tooth; tend, tendon of tongue, pulled back by m.card.ap.; to. tongue. (Partly 



after Tretjakoff.) 



respiratory tube is a series of velar tentacles, corresponding exactly in 

 position to those of amphioxus, and serving to separate the mouth 

 and oesophagus from the respiratory tube while the lamprey is feed- 

 ing. The seven branchial sacs are lined by a folded respiratory epi- 

 thelium and surrounded by muscles, and these, together with the 

 elastic cartilages and appropriate valves, ensure the pumping of the 

 water tidally, in and out of the external openings. In front of the first 

 sac is the remains of an eighth pouch, whose surface is not respiratory. 

 The 'salivary' glands are curious organs of which little is known. 

 They are a pair of pigmented sacs, embedded in the hypobranchial 

 muscles. Each has a folded wall, from which a duct proceeds forward 

 to open below the tongue. The salivary glands produce a secretion 

 that prevents coagulation of the blood of the fishes on which the lam- 

 prey feeds. The nature of this secretion is not known, but it rapidly 

 turns black on exposure to the air and the glands for this reason 

 appear to be pigmented. It has been observed that in lampreys taken 

 from fishes the intestine is filled with red corpuscles, and there is 

 therefore no doubt that they feed mainly on the blood of their prey. 



