OCT. 1895. VERTEBRAL COLUMN OF AMIA HAY 25 



5. THE ORIGIN AND DEVELOPMENT OF THE VERTEBRAE OF AMIA DURING 



ITS EARLY STAGES. 



Since my results obtained from the study of adult specimens 

 have been put in practically the form presented above to the reader, 

 I have had the good fortune to acquire a considerable amount of lar- 

 val and young material. Some of this, consisting of larvae from 10 

 to i5mm. in length, was received from Dr.J. E. Reighard, of the Uni- 

 versity of Michigan, through the kind offices of Dr. Eycleshymer, of 

 the University of Chicago. For the possession of the young of larger 

 growth, varying from 23 to 44mm., I am indebted to Dr. S. A. 

 Forbes, of the University of Illinois, and his assistant, Prof. Frank 

 Smith. The University of Illinois supports a biological station on 

 the Illinois river at Havana; and it was here that Prof. Smith secured 

 the materials sent me. As a result of a study of the young of Amia, 

 I am able to throw some light on the development of its vertebral 

 column, and that of fishes in general. 



I have prepared transverse and sagittal sections of specimens 

 lomm. in length. An enlarged figure of a specimen of this length 

 may be found on PI. xxx. of Mr. Allis's paper on Amia (i.) In 

 specimens of this size the notochord is already vacuolated. The 

 walls of the vacuoles stain deeply with carmine, but not, at least for 

 me, with hsematoxylin. Peripherally they pass into a layer resem- 

 bling in every way themselves, but thicker. The thickness of this 

 external layer I make to be about .oo66mm. but it is thicker where 

 the vacuole walls enter it. It apparently represents the epithelial 

 layer, which is seen at a later stage, but I find in it no traces of nu- 

 clei, or little else to suggest the presence of cells. Outside of it lies 

 a highly refractive, extremely thin layer, one of the sheaths of the 

 notoehord. 



Anteriorly the pointed end of the notochord is buried in the' con- 

 nective tissue closing in the pituitary space, but the greater portion 

 of the cranial division is enclosed in the well developed cartilage at 

 the base of the skull. This cartilage may be followed backward, in 

 longitudinal sections, into the two ridges of the skeletogenous tissues 

 which give origin to the upper arches. The specimens of the length 

 being considered do not all appear to be in the same stage of devel- 

 opment. In one examined the most anterior upper arches consist of 

 [hyaline cartilage. In another, the cartilage at the base of the skull 

 passes insensibly into procartilage in the region of the neural arches. 

 In the intervals between the nerve roots may be seen the bases of the 

 upper arches, distinguished apparently only by being slightly more 



