RELATIONSHIP OF AMMOCCETES TO OSTRACODERMS 35 I 



appendages. At present we have not sufficient evidence to decide 

 this question. 



That the animal crawled about in the mud by means of free 

 appendages is by no means an impossible view, seeing how difficult 

 it is to find the remains of appendages in the fossils of this far-back 

 time, even when we are sure that they existed. Thus, for many 

 generations, the appendages of trilobites, which occur in such count 

 less numbers, and in such great variety of form, were absolutely 

 unknown, until at last, in consequence of a fortunate infiltration 

 by pyrites, they were found by Beecher preserved down to the 

 minutest detail. Even to this day no trace of appendages has been 

 found in such forms as Hemiaspis, Buuodes, Belinurus, Prestwichia. 



The whole question of the evidence of any prosomatic appendages 

 in these ancient fishes is one of very great interest, and of late years 

 has been investigated by Patten. It has long been known that 

 forms such as Pterichthys and Bothriolepis possessed two large, jointed 

 locomotor appendages, and Patten has lately obtained better speci- 

 mens of Bothriolepis than have ever been found before, which show 

 not only the general configuration of the fish, but also the presence 

 of mandibles or gnathites in the mouth-region resembling those of 

 an arthropod. These mandibles had been seen before (Smith Wood- 

 ward), but Patten's specimens are more perfect than any previously 

 described, and cause him to conclude that these ancient fish were 

 of the nature of arthropods rather than of vertebrates. 



Patten has also been able to obtain some excellent specimens of 

 the under surface of the head of Tremataspis, which, as evident in 

 Pig. 143, show the presence of a series of holes, ranging on each side 

 from the mouth-opening, in a semicircular fashion towards the middle 

 line. He considers that these openings indicate the attachments of 

 appendages, in opposition to other observers, such as Jaekel, who look 

 upon them as gill-slits. To my mind, they are not in the right 

 position for gill-slits ; they are certainly in a prosomatic rather than 

 in a mesosomatic position, and I should not be at all surprised if 

 further research justified Patten's position. So convinced is he of 

 the presence of appendages in all these old forms, that he considers 

 them to be arthropods rather than vertebrates, although, at the same 

 time, he looks upon them as indicating the origin of vertebrates from 

 arthropods. Here, perhaps, it is advisable to say a few words on 

 Patten's attitude towards this question. 



