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of the skull, lying immediately anterior to the articular facet for 

 the hyomandibular, and opening, externally, at the dorsal edge of 

 the lateral surface of the head. From the basal portion of this part 

 of the canal, on its antero-mesial surface, the spiracular diverti- 

 culum described by Bridge (1879, p. 697) is given off. Passing 

 through the foramen x of that author's descriptions, this diverticulum 

 enters the outer, posteriorly directed end of the f-shaped groove on 

 the dorsal surface of the skull, as Beidge has stated, and there 

 expands into a sac-like portion which contains two latero-sensory 

 organs innervated by branches of a nerve that has a course similar 

 to that of the r. oticus facialis of Amia. The diverticulum is a closed 

 pocket, and does not, even in my larvae, open on the superior surface 

 of the skull, as Bridge has stated that it does. In my youngest larva 

 there is a second perforation of the lateral wall of the skull, opposite 

 the anterior end of the diverticulum, but this opening is not found 

 in my older larvae or in the adult. Anterior to the anterior one of 

 these two openings, the cranial wall is traversed by the canal for the 

 r. oticus facialis, and this canal although not shown in Bridge's figures, 

 is found in each of the two adults I have examined. 



In Polyodon there is, accordingly, a spiracular canal that runs 

 upward along the outer surface of the skull and opens on the outer 

 surface of the head; and this canal has a diverticulum that traverses 

 a canal in the cartilage of the skull to reach its dorsal surface and 

 there expand into a sac-like portion that contains two sensory organs 

 that undoubtedly belong to the latero-sensory system. In Lepidosteus 

 (Wright, 1885) there is also a spiracular canal and a sensory diverti- 

 culum, but the spiracular canal is occluded, even in larvae, and does 

 not open on the outer surface of the head. In Amia (Wright, 1885) 

 the sensory diverticulum is found, but the spiracular canal, beyond 

 the point of origin of the diverticulum, has, even in larvae, wholly 

 aborted. In Acipenser (Wright, 1885) there is, as in Polyodon, spira- 

 cular canal, spiracle and diverticulum, but whether the diverticulum 

 contains sensory organs or not is not stated. If it does contain such 

 organs, the possession of this spiracular diverticulum, with well devel- 

 oped sensory organs, would seem to be a definite ganoidean characte- 

 ristic. For such a diverticulum has never been described in any 

 teleost, so far as I can find, and in Mustelus, where the diverticulum 

 is described by Wright (1885) and myself (1901), it is lined with an 

 epithelium which, while doubtless sensory, contains no definitely 

 developed sense organs. (Schluß folgt.) 



