Ryder.] 554: [Nov. 1, 



ably the vesicular connective tissue of mollusks falls into tlie same cate- 

 gory. 



The common character of all these types of tissue is the development of 

 cavities in its cells filled with fluid. All, except the last, also seem to 

 have lost the power of storing up plasma, and the plasmic cell walls be- 

 come thin and the nucleus is either pushed into a parietal position and 

 adherent to or embedded in the cell wall, as in the notochordal tissue, or 

 the nucleus is suspended by plasmic threads running radially from the 

 plasma which invests it to the attenuated wall of the vesicular cell. 



A mass or cord of such cellular tissue also possesses certain elastic prop- 

 erties as a result of which it may not only give form but also save the 

 expenditure of energy in the same way as we have already seen in the 

 case of the gelatinous matter of the umbrella of Medusae. Its elasticity 

 probably serves to automatically straighten out the body in youug fishes 

 or those in which the notochord is persistent, and thus saves the expendi- 

 ture of a great amount of energy through the metabolism of muscle. In 

 fact it is almost absolutely certain that the notochord of embryonic verte- 

 brates has the elastic properties which I ascribe to it, judging from the 

 phenomena exhibited while such embryos are dying under actual observa- 

 tion. It is a truly cellular supporting tissue in contradistinction to the 

 jelly-like matrix which makes up most of the sometimes slightly fibrous 

 substance of the umbrella of MedusfE. 



The elastic properties of notochordal and other vesicular supporting 

 tissues do not arise as in the gelatinoid non-cellular supporting matrix 

 from an inherent elastic property such as would be met with in a mass of 

 rubber or a jelly prepared from gelatin, but from the qualities arising from 

 a cord or mass of minute cellular vesicles, with rather firm walls, bound 

 together by intercellular substances and external culicular and intercellu- 

 lar membranes, investing such an aggregate of hollow cells. Such a me- 

 chanical aggregate possesses somewhat the properties of erectile tissue, the 

 qualities of which depend upon turgescence. In the latter case it is tem- 

 porary vascular turgescence under the control of the nervous system, and 

 consequently involves the expenditure of energy through metabolism, 

 both nervous and muscular, whereas in the former case the permanent 

 erection of the tissue is due to the permanent turgescence of the tensely 

 filled individual cells and calls for apparently no expenditure of energy. 



Another property of such vesicular tissues is their passivity or meta- 

 bolic indifference, which is obvious from simple inspection. This indiffer- 

 ence or metabolic passivity is also exhibited en masse, since there is inva- 

 riably a tendency to form more or less homogeneous fibrous or dense cutic- 

 ular membranes around such masses or cords of cells. This is the 

 expression in the living normal organism of the same phenomenon as the 

 deposition of a cuticular capsule around a sliver or bullet which has pen- 

 etrated and become permanently embedded in the comparatively indiffer- 

 ent or passive connective tissues of a higher animal, or the deposition of 

 a cuticuiar laminated capsule around Trichina3 lying between muscular 



