282 KEY TO TERRESTRIAL HISTORY 



strongly in favour of these organisms having lived near 

 or upon the spot where they are now found fossil, that 

 some wider-reaching theory seems to be demanded ; and 

 some geologists have not hesitated to cut the knot by 

 imagining some distribution of the land and sea, specially 

 designed to favour migration in desired directions. 



FIG. 86. A Graptolite (Diplograptus foliaceus, MacCoy) in various 

 stages of growth. 



1. The youngest form. ( x 3.) 



2. A young adult, showing very young individuals within the 



reproductive vesicles (gonothecee) and fully formed branches 

 of different age. ( x 3.) 



3. A colony in which all the branches belong to a single 



generation, (x f.) 



4. Similar, but showing the swimming bladder, pneumatophore 



(the rounded body in the middle), surrounded by gonothecse. 

 / Y 9 \ 

 ( x TV 



5. A fully grown colony, with the pneumatophore in the centre, 



surrounded below by gonothecse, and supporting several 

 whorls of branches of different age. (x f.) After Ruedemann. 



Indeed, there exists a considerable body of independent 

 evidence to show that these imaginary distributional areas 

 did, at least in part, actually exist. No one now doubts 

 the wide extension of the Mediterranean in Jurassic 

 times, when it spread through the heart of Europe and 

 Asia. Along the shores of this ancient Tethys, as Pro- 

 fessor Suess names it, the Ammonites of the Jurassic 



