198 FREDERICK TILNEY AND LUTHER F. WARREN 



the adult (Warren 416 in Necturus, Osborn 289 in Siredon, Siren 

 and Proteus.) It is an elaborately folded, glandular structure 

 (Burckhardt 43 in Triton and Ichthyophis) , a solid vascular 

 mass (Sorensen 361 in Menopoma), or a tubular and digitated 

 structure (Eycleshymer 112 in Amblystoma). In Rana, accord- 

 ing to Minot, 277 the paraphysis is characterized by a glandular 

 epithelium, a tubular arrangement of its cells, and an appar- 

 ently sinusoidal circulation, In Lacertilia (Warren 415 in Lacerta 

 muralis, L. agilis and L. viridis) it is large and glandular in 

 character, forming a conspicuous element of the pineal region. 

 In many instances it is so extensive as to reach caudad as far 

 as the midbrain, or even the cerebellum. In ophidians, chelo- 

 nians and crocodilians, the paraphysis is small and rudimentary. 

 In birds it was first demonstrated in the chick by Selenka 352 and 

 later described by Minot 277 in the chick and Burckhardt 46 in 

 the embryo crow. Dexter 90 found it constant in the chick and 

 common fowl. He believes it to be a gland in which there are 

 no sensory elements. 



In mammals Selenka 352 gave the first description of the para- 

 physis in the opossum. Francotte 128 observed it in a 12 mm. 

 human embryo. Usually, however, although it has been recog- 

 nized in anlage, in mammals it disappears early and the para- 

 physeal arch bears no trace of it in the 'fetal period. 



Thus it will be seen that the glandular nature of the para- 

 physis in the middle portion of the phyletic series, including 

 amphibia and lacertilia, is quite beyond dispute. Some of this 

 character it retains in the more modern reptiles and birds. On 

 the other hand, it is relatively inconspicuous as an organ among 

 the lowest vertebrates and disappears altogether is most mam- 

 mals. Manifestly, therefore, whatever tendency toward speciali- 

 zation the paraphysis presents is in the interest of glandular 

 formation. As a gland, it appears either to contribute its secre- 

 tion directly to the cerebrospinal fluid in the ventricles or in- 

 directly to the blood. In no instance is there evidence of a 

 tendency toward the development of sensory structure nor do 

 the histological elements entering into the paraphysis suggest 

 its direct participation in any neural mechanism. 



