94 On the Morphology of the Pineal Region 



a well defined paraphysal arch in front of the velum and post-velar arch 

 behind it. In a jSTecturus of 15.0 mm. (Sagittal series 79, section 84) 

 the paraphysis is a narrow elongated evagination from the arch, and 

 so appears again in embryos of 18 mm.. Fig. 13. In embryos of 21 mm. 

 the wall of the paraphysis is irregular, and in a larva of 26.0 mm. the 

 anlages of the paraphysal gland tubes are easily recognized (Sagittal 

 series 377, section 12G). 



In the chick the paraphysis is developed very late and at seven days 

 is a small nearly hemispherical evagination. Fig. 14, Par., formed from 

 the paraphysal arch, P, quite near the rudimentary velum, V. A day 

 later the epithelium is thicker and irregular as if the glandular tubules 

 were beginning to form. 



In Petromyzon Burckhardt figures a small evagination, which is prob- 

 ably the paraphysis, but his figure does not show the limits of the para- 

 physal arch. In various forms it is known that the paraphysis arises 

 as a small evagination, which appears just in front of the velum and 

 rather late in development as a local outgrowth. See for example 

 Kupffer's observations on Accipenser; the observations of de Graaf, 

 Burckhardt, Eycleshymer and others on Amphibia, those of Dendy and 

 Burckhardt on reptiles. In all these cases there is a comparatively 

 wide paraphysal arch, and a small paraphysis. The two things have 

 heretofore not been distinguished so that there is considerable confusion 

 in the descriptions. 



The existing observations render it probable that the paraphysis is a 

 true gland, the main evagination serving as the duct, while the secon- 

 dary tubules are the secretory portions. Certainly the type of organi- 

 zation is that of a gland and not of a sense organ, and whenever the 

 adult paraphysis has been found and studied it has presented the same 

 plan of structure. Its secretion must of course pass into the cavity of 

 the brain, so that functionally it is comparable to the glandular epi- 

 physis in birds, and the infundibular gland of all vertebrates. One 

 may suppose that these three glands supply some substances, which are 

 useful to the nervous system, and that they are somewhat comparable 

 from the physiological standpoint to the ductless glands at least in 

 respect to the fact that their secretion has no direct open channel of 

 escape from the body. 



The velum probably is characteristic of all vertebrates. In elasmo- 

 branchs the post-velar arch remains small, hence the velum seems to 

 arise later very close to the mouth of the epiphysis. In ganoids the 

 post-velar arch is well developed, hence the velum is inserted quite far 

 in front of the epiphysis. As regards the teleosts the data for a satis- 



