MUSTELTTS L.EVlS. Ill 



the posterior oues lie lateral to that caual^ extending nearly 

 to the anterior edge of the eye, certain of the tubules here 

 lying superficial to the tubules of a sub-group of the outer 

 buccal ampullge. There were twenty-five pores in this group 

 on one side of the head, and twenty- one on the other. 



The relations of the tubules of this sub-group of ampullse 

 to the supra-orbital lateral canal is exactly that that would 

 necessarily arise in every place where the ampulla and its 

 pore lie on opposite sides of a lateral canal if the ampullary 

 tubules were formed by the pores travelling from the place 

 where the ampullary organ was first enclosed by involution, 

 after the manner of development of the canals and tubes of 

 the lateral system in Amia (2). I accordingly turned to the 

 sections of my 55 mm. embryo to see if I could determine 

 whether these particular ampullar lay postero-lateral or 

 antero-mesial to the supra-orbital canal, and I found, as I 

 had expected, a number of the teat-like processes that here 

 represent the ampullae in exactly the position that the pores 

 of the group in question occupy in the older embryo. These 

 teat-like processes were directed anteriorly, as they should be, 

 aud in my opinion unquestionably represent the ampullas of 

 the older embryo, though this can certainly not be positively 

 asserted until they have been followed through certain of 

 the intermediate stages. Why these particular ampuUfee 

 should have pushed forward external instead of internal to 

 the lateral canal is not evident. 



The tubules of the posterior sub-group of superficial 

 ophthalmic ampulla3 arc, in part, still longer than those in 

 the second sub-group. They all at first run postero-laterally 

 from their ampulla3, the longer ones gradually turning 

 directly backward. Most of them have their external 

 openings in a line slightly mesial to that part of the supra- 

 orbital canal that lies directly dorso-mesial to the eye, but 

 some of them lie scattered between that line and the mid- 

 dorsal line of the head, and six of them form a curved line 

 which lies slightly anterior to the supratemporal cross- 

 commissure, and slightly anterior also to the ti-ansverse 



