302 



ganglia of V, VII, and VII lateralis this nerve arises from in Lepi- 

 dosiren. According to Pinkus in Protopterus the part of the gan- 

 glionic complex supplying the lateral line system of the Vllth nerve is 

 distinguished from the facial and trigeminal ganglia proper by its 

 larger cells with less granular nuclei. A similar histological distinction 

 is found in Lepidosiren. I can only say with certainty that some at 

 any rate of the fibres of the nerve supplying Pinkus' Organ in Lepi- 

 dosiren arise from the posterior ventral region of the small celled 

 portion of the ganglionic mass, i. e., from the Facial ganglion. 



In stage 35 the squamosal bone is beginning to develop, and the 

 nerve runs between this and the cartilaginous wall of the auditory 

 capsule. 



At about stage 36 a hoop of cartilage is formed round the organ, 

 which now lies mainly in the space included between this and the side 

 of the cartilaginous cranium, being covered over dorsally by the squa- 

 mosal. 



Later stages are concerned mainly with the dwindling of the 

 hypoblastic strand and the completion of the histogenesis of the organ. 

 This soon becomes T-shaped by the ongrowth of an anterior and a 

 posterior lobe. Its shape is thus similar to the same organ in Proto- 

 pterus. 



In stage 38 (about 3 months after hatching), which was the oldest 

 of the heads examined by means of sections, the remains of the original 

 hypoblastic connection with the Pharynx has interesting relations. The 

 efferent artery from the hyoideau hemibranch runs at first parallel to 

 the internal carotid, but at the level where this vessel enters the skull 

 the hyoidean artery turns at a right angle to join it. The median 

 tube of Pinkus' Organ is continued inwards as a fine but very well 

 marked strand of cells which curves round the front surface of the 

 hyoideo-mandibular nerve, and ends in a swollen knob intimately applied 

 to the wall of the efferent hyoidean vessel at the point where it turns 

 inwards to run into the internal carotid. Pinkus does not mention 

 a similar connection with the hyoidean artery in Protopterus. 



In the adult the organ comes to lie far behind the hyoid. This 

 position, however, is secondary. At earlier stages it lies in front of 

 this arch — in fact in stage 25, owing to the shortness of the front 

 part of the head, the spiracular rudiment lies under the optic vesicle. 



An organ dissected out of an adult head showed the following 

 histological features. The greater part of the organ is lined internally 

 by a flat epithelium. Along a line extending a great part of the length 

 of the antero-posteriorly directed portion of the organ this epithelium 



