Notes on the morpholoscy of the Tunicata. 555 



very slightly developed, are found in the glands of Boltenia and of 

 Salpa africana-maxima. The presence, rarely, of blood corpuscles in 

 the gland or funnel and of trabeculae of connective tissue in the 

 gland in a few forms is not enough to bear out an interpretation of 

 the neural gland as a lymph gland, though it did suggest careful 

 examination of this point. 



The gland is evidently functional in the Tunicata, but what its 

 function is we cannot at present say. 



I have several times referred to the great divergence between 

 species in the character of the neural gland. There is, however, no 

 great amount of variation in the gland of a given species. A high 

 degree of variation in the gland might be regarded as evidence 

 that it was of slight functional importance. The divergence de- 

 scribed, of course, should have no such interpretation. 



JuLiN ^), nearly 20 years ago, suggested that the Tunicate neural 

 gland is the homologue of the hypophysis in Vertebrates. We have 

 some data for judging of the correctness of the suggestion. The 

 Tunicate neural gland arises from the central nerve tube; its duct is 

 the persistent anterior part of this nerve tube; its aperture is the 

 modified neuropore; its secretion is formed by the disintegration of 

 cells proliferated from the endothehum of the gland. In the light of 

 these four characteristics how great is the probability of any homo- 

 logy with the hypophysis? HALLER,.in a recent fine paper on the 

 hypophysis of the Vertebra ta-), has shown, more clearly than was 

 ever before demonstrated, that that which has been called the hypo- 

 physis consists of two distinct portions, one of which, the hypophysis 

 proper, is derived from the stomodaeal ectoderm, while the other, the 

 Saccus vasculosus or infundibular gland, arises from the wall of the 

 infundibulum. The infundibular gland pours its secretion into the 

 cavity of the infundibulum : the hypophysis proper empties its secretion 

 into the space between the two investing membranes of the brain. 

 Speaking in one place of the hypophysis of Selachians Haller says: 

 "Der Hypophysenkopf" (the upper more soHd portion of the hypo- 

 physis proper) "besteht aus weiten, zum Theil auch doppelten und 

 dreifachen Schläuchen, mit sehr deutlichem Lumen, welcher mit 

 Detritus von abgestossenen Zellen oder mit Secret er- 

 füllt sein kann"3) (1. c. p. 75). 



1) JULIN, 1881. 



2) Hallbr, 1896. 



3) The emphasis on the last clause is my own. 



