14 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 54 



ceeds the paraphysis becomes elongated until, in embryos of 7 cm. 

 length, it is seen as a tubular structure, with nearly smooth walls, 

 slightly curved away from the cerebral hemispheres and over the 

 top of the diencephalon. In embryos of 13 cm. the paraphysis has 

 practically the same structure as in the 7 cm. embryo. 



The velum grows forward into each lateral ventricle to form its 

 choroid plexus. 



The hypophysis in the alligator begins, at about the same stage 

 as does the paraphysis, as a single, median evagination of the roof 

 of the mouth, just beneath the floor of the infundibulum. The 

 original evagination becomes the stalk of a considerably branched, 

 hollow structure which, by the lengthening of the stalk, recedes to 

 some distance from the roof of the mouth. The stalk becomes solid 

 and finally loses all connection with the oral epithelium. The body 

 of the hypophysis also becomes almost completely solid, in an embryo 

 of 13 cm., and is seen as a lobulated mass of lymphoid tissue lying 

 close under the floor of the infundibulum. 



The material upon which this work has been done was collected 

 by the writer, in Central Florida, with the aid of a grant from the 

 Smithsonian Institution, for which grant acknowledgment is here 

 made. 



