QUARTERLY CHRONICLE OF MICROSCOPICAL SCIENCE. 177 



the influence of acetic acid, other parts undergo, and thus 

 the appearance of an interrupted membrane is produced. 

 While this is the usual structure, there may be parts where 

 the nuclei and tibres are entirely wanting, and an appearance 

 may thus be produced corresponding to the descriptions of 

 Keichert and Miiller ; if, again, such a membrane as here 

 described should be perforated at some points, a reticular 

 structure would result, such as described by Rollet and 

 Henle. 



Sometimes a more or less incomplete investment of the 

 bundle, by means of flat polygonal cells, is seen, which 

 often show a transition to a stellate form, and the processes 

 of which also pass into the substance of the membrane. The 

 gaps left in tlie sheath Boll believes, at all events, in part 

 belong to the original structure. Finally, there are some 

 bundles which are covered with small coarsely granular and 

 protoplasmatic cells, corresponding in shape to those Avliich 

 have been described as occurring in diflerent parts of the eye 

 by Leber, Iwanoff", and llollet. It has been suggested by the 

 latter observer that such cells may l)e white blood-corpuscles ; 

 and Boll, in order to throw some light upon this question, 

 which could not be decided by hardened preparations, made 

 some observations by means of the hot stage, but could not 

 arrive at any positive conclusion. 



Development of Fibrillated Connective Tissue. — The second 

 part of Boll's researches is occupied with the question of deve- 

 lopment of connective tissue, and especially the much-disputed 

 ])oint whether the fibres are, as originally supposed by 

 Schwann, formed by a metamorphosis of the cell itself, or 

 whether from the amorphous intercellular substance ? 



His investigations were chiefly conducted on the em- 

 bryoes of birds, especially the common fowl and the sea-gull. 

 The mammalian embryo was not eqtially suitable on account 

 of the necessity of using perfectly fresli, still warm objects. 

 The fowl's embryo was found to be suitable for observation 

 only for a single hour. The examination was conducted on 

 small fragments immersed in amniotic fluid. 



The cerebral arachnoid, which Avas one of the tissues 

 studied, was found to consist, on the third day of incubation, 

 of closely set elongated cells, which showed at each pole 

 something resembling a short fibre. On the fourth day, in 

 isolated cells, the terminal parts of the cell show no longer 

 a purely granular protoplasnia, but small rough fibrillge 

 are seen to extend between the single granules. Later on 

 the cells become more and more widely separated, Avhile a 

 perfectly clear homogeneous mass, the " iutercellular sub- 



