The Brain of Diemydylus Vii'idescens 279 



tracts, and their exact processes of growth, determined b}- 

 finer methods, a more complete correlation of brain structure 

 with these crises may be found. 



PART II. PLATE VIII. 



COMPARISONS WITH AMIA AND LAMPREY. 

 MATERIAL. 



The brain in the skull of Amia calva was prepared, sectioned 

 and drawn by methods described for diemyctylus. Twelve 

 series of larval Petromyzon* were cut, some after hardening in 

 picric alcohol, but the more successful preparations were 

 hardened in mercuric chlorid. 



The sections made agree in most particulars with the fig- 

 ures of Ahlborn (i) of lamprey and Goronowitsch (21) of the 

 amia. The drawings presented add certain details, show 

 somewhat different structure or are necessary to illustrate the 

 comparisons here made. The reconstructed mesal views show 

 certain features not before noted. 



A detailed account of the figures is given in the explanation 

 of Plate VIII, hence a consideration ot special points will be 

 at once entered upon. 



METAPORE. 



Wilder (54) has demonstrated that in the adult man and 

 certain apes, in the caudal region of the metaplexus, there is 

 a lack of continuity in the endynia and pia, thus placing the 

 cavities of the brain in communication with subarachnoid 

 spaces. In lower forms such an opening has been considered, 

 from an embryological standpoint, as highly improbable, no 

 such break being found in early stages. In the amia (Fig. 

 93) a pocket of endyma extends caudad from the metaplexus 



* It is impossible to state whether these were larvse of Petromj'zon 

 niariniis or of Ammocsetes (Petromyzon) brauchialis, since both lay 

 their eggs in the same streams and even the same nests, as shown in an 

 article by S. H. Gage in this volume. 



