Jxoijal Mieroscojncal Society. 213 



the fiftli or gill-less arrested arch. Here the primordial form serves 

 throughout life, and is very gently specialized for life-function. 

 But it was the first pair which most struck me with the beautiful 

 ^n'ospedive harmony between morphology and final purpose, for the 

 same curve inwards at the top, which is so apt for the formation of 

 the crushing apparatus of the fish's throat, here serves to wall-in the 

 pilnitary body, and thus form the primordial " Sella turcica " or 

 Turkish Saddle. Again, the next arch, which crescent-like, forms 

 an elegant ledge for the huge eye-ball to rest upon — this arch must 

 needs, as soon as it is freed from the pressui'e of the precocious 

 visual organ, curve itself inwards at the top. By doing this, it 

 exactly applies itself to the front edge of the succeeding arch, to 

 which it is soldered in a week or two after hatching. The arch of 

 the lower jaw and the arch of the tongue have the same advan-' 

 tage in the upper hook, and all the secondary attachments and 

 delicately beautiful adaptations, as they become specialized, all 

 these, I say, give voice to the morphological importance of the 

 primary curve. It would be endless to go into the use of the facial 

 arches in the various tribes, for, when there are no gills developed, 

 as in reptiles, birds, and mammals, the two pairs of horns attached 

 to the bone of the tongue (hyoid), the arch of the lower jaw, the 

 arch of the palate, and all the base of the nasal septum, and of 

 the skull itself, as far backwards as to the exit of the optic nerves 

 — all these parts are derived from the simple S-shaped facial 

 rods. But there is an exquisite instance of special use which I 

 cannot pass over; it is in the class of birds. In these, as in all 

 vertebrates above the amphibia (newts and frogs), the only gill- 

 arch developed is the first, and this is gill-less, but is made to 

 subserve other functions. In most bu-ds, this arch reaches as far as 

 the occipital plane, but in humming-birds and woodpeckers these 

 horns are of extreme length and slenderness, and reach as far as to 

 the fore-end of the cranial roof. These elongated rods form the 

 skeleton of the long worm-like protrusible tongue, and enable it to 

 be shot out without a moment's notice, so that the nimblest of 

 insects are caught "or ever they are aware." A function so new in 

 a gill-arch would seem to ask for a large amount of metamorphic 

 change of form. It is not so ; this arch in those birds retains 

 exactly its primordial curve. We must still study form free from 

 all final purpose, bias, and j)reconception ; but a new and delightful 

 phase of teleology wiU set in when the laws of foi-m have been 

 mastered. A man may run whilst he is reading the large plain 

 characters in which final purpose is written, but he must be as 

 good a sitter as the best hen in a farmyard if he would add any- 

 thing of value to the science oiform. 



