190G.] KEllVES OF CHLAMYDOSELACHUS ANGUINEUS. 965 



begins somewhat above the level of the eye, but does not extend 

 quite as far ventrally as the level of the mouth. This group 

 cannot be considered the equivalent of the mandibular ampullfe, 

 for it is innervated by a number of small branches from the ramus 

 buccalis. It may be called a postero-buccal group of ampullfe in 

 order to bi-ing its nomenclature into line with that of the other 

 group innervated by the r. buccalis. This group may correspond 

 to the occipital row of ampullfe in Chimcera (3. p. 655), parts of 

 which were innervated by a bi-anch of the r. oticus. There is in 

 Chlamydoselachus no repi-esentative of the mandibular group. 

 The latter may in Elasmobranchs have arisen as a caudad offshoot 

 of the postero- orbital group, which, owing to its position, acquired 

 a hyomandibular innervation. On the other hand, the mandi- 

 bular group may have ai'isen independently of a group such as 

 the postero-orbital, coincident with the disapjjearance of the 

 latter. 



A third, very diffuse group of openings occurs along the upper 

 jaw immediately above the mouth. It extends from the anterior 

 extremity of the head almost to the angle of the raouth. The 

 group is innervated by numerous branches from the r. buccalis, 

 and is no doubt homologous with both the outer and inner buccal 

 groups of ampullfe of the higher Elasmobranchs, if we are to 

 consider with Allis (1. p. 93) " tliat the sui-face ampullary pore 

 represents approximately the place of origin of the ampullary 

 organ." The group may be called the buccal group. 



A fourth, very small group occurs at the symphysis of the lower 

 jaw. The number of openings in this group varied from one to 

 nine in the specimens examined. This group is innervated by a 

 branch of the hyomandibular nerve, and represents the hyoid 

 group of the Elasmobranchs. 



It is evident, on close inspection, that what appears to be a 

 single ampullary opening is in reality a group of openings placed 

 closely together in an area devoid of scales. The number of 

 openings in each group is usually four, but may be reduced to 

 two or increased to six. When traced inwards each opening is 

 found to lead into a thin-walled tubule, the tubules from each 

 group of openings being united. Each tubule terminates in a 

 number of ampvdlary pouches. A complete group is never more 

 than 5 mm. long and lies almost parallel to the surface of the body. 

 Each group is independent, so that the term " group of ampullte " 

 represents in this species a very different anatomical entity from 

 what it does in the majority of Elasmobranchs. In Chlamydo- 

 selachus there are many sujoerficial scattered groups of minute 

 compound ampullae, which together represent the usual, single 

 deep-seated group of much longer simple ampullae. The small 

 groups here may be compared with those described by CoUinge in 

 Chimcera (5. fig. 9, B). The tubules are almost transparent, 

 having very thin walls, consisting of a single layer of flattened 

 cells. The cells pass gradually into the columnar cells which 

 line the ampullary pouches. The latter cells have the granular 



