or THE EARLIER VERTEBRATA. 55 



raediateiy between tlie eyes, or a very little over them. Its 

 never-failing recurrence shows that it must have had some 

 meaning, though it may be difficult to say what* In the 

 Coccosteus it takes the form of the male dovetail, which united 

 the nasal plate or snout to the plate representative of the su- 



* I had the pleasure, in the autumn of 1850, of introducing Professor 

 Owen and Sir Philip Egerton to vaj collection. Both gentlemen ex- 

 pressed a desire of seeing the little plate referred to here, as exhibited in 

 the cranial buckler of the Diplopterus, and I submitted it to their in- 

 spection in a specimen which — wholly detached from the rock — exhibits 

 it both in the outer and inner surface of the buckler. " It is exactly as 

 1 had thought," said the distinguished comparative anatomist to Sir 

 Philip, " a prolongation of the brain extended downwards from the 

 brain-pan proper, and bore at its termination the pineal gland, which 

 rested immediately under the little plate, and had its place indicated by 

 it." The revelation struck me as fraught with a startling interest. A 

 disciple of that ancient school of anatomy which regarded this gland as 

 the seat of the soul would have said that the ever-recurring plate which 

 had attracted my notice marked the exact point where the soul of an 

 ancient fish of the Old Red Sandstone took its stand, — ^like the man sta- 

 tioned a-head on the outlook in a vessel, — to will and direct the crea- 

 ture's course. During my subsequent exploratory labours among the 

 rocks of Caithness I kept the remark of Professor Owen in view, and 

 succeeded in procuring, through the kindness of Mr Dick, part of a cra- 

 nium of Diplopterus, which illustrates, and — so far at least as the solid 

 and less perishable parts of an organism can confirm so occult a conclu- 

 Bion regarding the soft and perishable ones — confirms it. In the speci- 



Fig. 18. 



men figured (No. 18), the occipital and parietal portions of the buckler 

 tare been removed by a singularly delicate operator, — the slowly disin- 



