AS AN INDEX OF AGE. 25 



of the scale. Vogt thought the radiating lines as difficult to explain in young 

 as in adult scales, and Blanchard regarded them as canals which had connec- 

 tion with the supposed respiratory function of scales. Dr. Salbey thought 

 that they Avere excavations of the superior layer aiding the growth of the 

 scale in surface extent. It appeared necessary to Baudelot to abandon all 

 these interpretations of the grooves on scales. From his observations he held 

 the following view : " The grooves of scales ought to be considered as lines or 

 zones of non-calcification, that is to say, as lines to the level of which the 

 calcification of the exterior layer of the scale has not taken place." The 

 exterior layer has centres of calcification which later unite with each other as 

 these centres extend. " When the union of the centres of calcification takes 

 place from the centre of growth towards the periphery and occurs at the same 

 time in the transverse direction, that is to say, parallel to the external contour 

 of the scale, there result radiating grooves ; when, on the contrary^, the union 

 of calcigenous centres takes place parallel to the contour of the scale, without 

 having taken place at the same time in the radial direction, transverse or con- 

 centric grooves result. "When the union of calcigenous centres fails to take 

 place both in the radial direction and transversal direction (parallel to the 

 external contour of the scale) at the same time, there results the simultaneous 

 existence of radiating and concentric grooves. Lastly, when the union of 

 calcigenous centres takes place without order and symmetry, the surface of the 

 scale shows grooves arranged in a more or less irregular manner. It is hardly 

 necessary' to add that when the union of centres of calcification takes place 

 completely in all directions, there is no further trace of grooves at the 

 surface of the scale." 



7. The perforating canaliculi. Under this term Baudelot described for the 

 first time extremely small canals which traverse the scale through and through 

 from the upper to the under side. Baudelot firstly observed these perforat- 

 ing canaliculi in the carp ; but found them later in many other fish scales, 

 both cycloid and ctenoid. These perforating canaliculi are only found in the 

 posterior area of the scale. In some types of scales they are easily observed, 

 in others only with difficulty. In the scales of the carp the perforating 

 canaliculi open externally in connection with the radiating canals of the 

 posterior area, and traverse the scale through to the under side in a slightly 

 ol)lique direction, and terminate internally on the inferior surface of the scale. 

 This internal opening or ostiole is usually nearer the posterior border than the 

 external ostiole, and further, if one takes a line down the middle of the scale, 

 one finds that the internal ostiole is further from this axis than the external 

 ostiole. In Mwjil cephalus the canaliculi round the centre of growth present 

 certain peculiarities which are notevvorthy. They traverse the scale more 

 obliquely, and have a larger diameter. At the external surface these canali- 

 culi open into grooves or trenches and pass on towards the large canal, which 

 in Mugil occupies the centre of each scale. The grooves in connection there- 

 with anastomose with each other, and gradually enlarge as they approach the 

 median canal, where tliey terminate by bending into a spout-like or canali- 

 cular orifice. The large canal in the centre of the scale should be considered 

 as a species of collector in connection with the nearest adjacent canaliculi. 



