On the Microscopic Structure of the Scale of Amia Calva. 95 



characteristic and unlike ordinary lacunse, d with its elongate and 

 more tapering form and fewer canaliculi is assuming a more 

 normal appearance, and e is still more normal, having altogether 

 lost its short abrupt lateral branches, and only presenting very 

 fine and tapering terminal ones. At the margin of the scale we 

 find lacunae of this kind alone (fig. 5), differing from each other 

 only in respect of their length, number and extent of canaliculi, 

 &c, and reminding us of the well known lacunse of the allied 

 Lepidosteus osseus (fig. 6) which are figured in most books 

 on microscopy. They differ from them, however, in being much 

 larger, less globular, and having much wider canaliculi which do 

 not anastomose to the same extent ; whilst the scale itself does 

 not exhibit any of the canals running in from the surface which 

 seem to be constant in the scales of Lepidosteus. There do not 

 appear to be any lacunae in the posterior part of the scale from 

 about c d backwards, in front of this line they begin as small 

 simple forms like e, fig. 4, and <x, fig. 5. 



Explanation of the Plates. 



Fig. 1. Entire scale of Amia calva magnified 5 diameters, showing the finely toothed 

 posterior edge, the general direction of the ridges, and the position of the characteristic 

 lacunae. The line a b indicates the place where the ridges tend to run into each other, 

 c d the level behind which no lacunae are found. 



Fig. 2. A portion of the posterior part of the scale showing the nature of the ridges 

 and the toothed border, X 90. The arrows show the direction in which the light came, 

 oblique illumination having been used. 



Fig. 3. Lacunae from the central part of the scale, X 180. At o is seen one in which 

 the central lacuna is linear ; b is one of the highly complex forms ; c and d have smaller 

 lacunar systems connected with them. 



Fig. 4. Lacunae occurring in the same field of view, X 260. Taken from a part of the 

 scale about half way between the centre and the margin ; a, 6, c, are of the characteristic 

 complex form, d and e are simple. 



Fig. 5. Lacunae from the marginal part of the scale, x 260. At a is seen one of the 

 simplest forms. 



Fig. 6. Lacunae from the scale of Lepidosteus osseus, X260 showing the small size of 

 the lacunae, their globular shape and very fine canaliculi. 



The drawings were all made under a Wollaston camera lncida. 



