1890.] natural sciences of philadelphia. 407 



November 4. 

 Mr. John H. Redfield in the chair. 

 Fifty-seven persons present. 



The functions and histology of the yolk-sack of the young Toad-fish. — 

 Prof. J. A. Ryder presented verbally some observations upon the 

 microscopic anatomy of the yolk-sack of the young Toad-fish or 

 Batrachus tail. Unlike the larv?e of other fishes, the young of this 

 form do not at once escajte from the egg-membrane when the latter 

 is ruptured at the time of hatching but continue to adhere for a 

 long period by means of an adhesive discoidal area on the under 

 side of the yolk-sack to the inner side of a similar area of the egg- 

 membrane which in turn is adherent by its external surface to some 

 foreign object such as the under side of a stone, which forms the roof 

 of the tiny cavern excavated by tlie parent at the time of oviposition. 



The origin of the adhesive matter which causes the eggs to ad- 

 here to foreign bodies was well understood to be ovarian, but the 

 origin of the adhesive matter covering the discoidal area on the un- 

 der side of the yolk-sack has not until now been explained. If the 

 cellular membrane covering the inferior pole of the yolk-sack be 

 carefully dissected off, it is found to be much thickened as compared 

 with the rest of the outer wall of the yolk. This thickening is found 

 upon, making vertical sections of the adherent area, to be due to tlie 

 vertical lengthening and modification of the substance of the outer 

 cells of the epidermis of this region, The peripheral ends of the cells 

 of the epidermis are in fact here seen to be much prolonged in the 

 form of a homogeneous, almost vitreous, looking material, which shows, 

 by the w^ay in which the ends of these cells are roughened or fract- 

 ured, that they effect the adhesion of the yolk to the egg-membrane 

 before alluded to by the speaker. 



The whole of the free surface of the epidermis covering the yolk- 

 sack is studded with scattered goblet or mucous secreting cells. At 

 the edge of the adherent area of the epidermis there seems to be 

 some evidence of the fact that these goblet cells are multiplied so as 

 to completely cover the adherent area of the yolk-sack. If this is 

 the case, wdiich seems very probable, the cells causing the adhesion, 

 for a time, of the yolk-sack and consequently the whole embryo, to 

 the inner side of the egg-membrane, have originated from a multi- 

 plication and modification of the mucous or goblet cells completely 

 covering the adherent area referred to. 



Another remarkable peculiarity of the yolk-sack of the young 

 Toad-fish is the presence of a layer of smooth muscular fibres under- 

 neath the epidermis and a2:)parently originating from the splanchnic 

 mesoblast. This muscular layer consists of two layers of spindle- 

 shaped muscular fibres. One of these layers has its fibres running 



