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imSTELUS LEVIS. 87 



The Lateral Sensory Canals, the Eye-Muscles, 

 and the Peripheral Distribution of certain of 

 the Cranial Nerves of Mustelus Isevis. 



By 

 F<1\vni'4l Pliol|><>< Alli«i, jiiii. 



With Plates 10—12. 



I HAVE recently had occasion to examine three series of 

 sections of the head of embryos of Mustolns Isevis, one of 

 them being an embryo 12'2 cm. long. It Avas not my inten- 

 tion, when these sections were prepared, to make any extended 

 study either of the lateral canals or of the cranial nerves of 

 the fish ; the investigation I had proposed relating entirely to 

 the innervation of the sensory organs of the ampulla?. I have 

 long had a very decided impression, opposed to that of most 

 workers on the subject, that these ampullary organs must be 

 genetically related to the terminal buds of ganoids and 

 teleosts rather than to the pit organs of those fishes ; and I 

 thought that I should easily be able to get some positive 

 evidence of this in the general course and position of the 

 nerves that innervate them in advanced selachian embryos. 

 This positive evidence I have wholly failed to get, for the 

 very simple reason that, in the main nerve trunks, I could not 

 distinguish in my sections the ampullary fibres from the 

 lateral canal ones. Disappointed in this at the very begin- 

 ning of the investigation, I nevertheless decided to quite 

 carefully trace the lateral canals and the nerves that inner- 

 vate them and the ampullae, as far back as my sections went, 

 that is, nearly to the level of the first gill slit. Careful con- 

 sideration of these observations has fully convinced me, 



VOL. 45, PART 2. — NEW SERIES. H 



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