.30 FIELD COLUMBIAN MUSEUM ZOOLOGY, VOL. i. 



lower side of the vertebras some rudiment of these supports, either 

 in the form of bone or dense connective tissue. 



But Scheele is not content merely to note the occurrence of these 

 connective tissue aortal supports. He regards them as being of great 

 morphological importance, the representatives of a series of arches, 

 .absent, so far as yet known, from all other Teleosts. They are called 

 by him " hsemapophyses, " not indeed homologous with what have 

 usually been called such in the tail of osseous fishes, but with the 

 lower arches in the tail of Selachians, Urodeles and Ganoids. Scheele 

 would have us believe that in Rhodeus there are present representa- 

 tives of three series of arches, viz.: (i) the neural arches, (2) the 

 ribs and their homologues in the tail which enclose the haemal canal, 

 .all of which he calls parapophyses, and (3) the vestigial ' ' haemapo- 

 physes." The latter have been inherited from the Selachians and 

 Ganoids, but have, with the alleged exception of those of Rhodeus, 

 "been lost in the Teleosts. The parapophyses, therefore, belong to a 

 .series of arches which are placed at a higher level in the body of the 

 iish, derived originally, indeed, Scheele claims, from the upper arches, 

 " Theile der obern Bogen." 



Now, there is not an argument advanced by Scheele for the pur- 

 pose of establishing his ideas regarding the aortal supports as repre- 

 sentatives of a hitherto unrecognized series of arches in Teleost 

 fishes, and as homologous with the lower arches of sharks, and Gan- 

 oids, and Urodeles, that will not apply with greater force to the car- 

 tilages which support the aorta in Amia. And yet it is perfectly ob- 

 vious that these processes from the parapophyses do not become mod- 

 ified in this Ganoid's tail into the lower arches. As we pass back- 

 ward in a series of cross-sections of an Amia 27mm. long, we find 

 that near the last dorsal vertebra, the cartilaginous bases of the lower 

 .arches assume in section a triangular form. The parapophyses arise 

 from the upper outward angle, the one pointing outward beneath 

 the peritoneum, the aorta supports from the lower inner angle. The 

 outer angle is plainly prolonged in the last dorsal vertebra ; \vhile in 

 the next vertebra, the first caudal, it is united with its fellow beneath 

 the caudal vessels. In short, the parapophyses are developed from 

 the upper portion of the bases of the lower arches, the aortal sup- 

 ports from the lower portion. The latter are simply differentiated 

 parts of the bases of the lower arches. 



In Fig. i o is shown a sagittal section through the axial region of 

 a specimen of Amia somewhat larger than the one just studied; it is 

 3omm. long. The section includes the anterior and a portion of the 

 middle tail region. The notochord and its two sheaths are repre- 



