DEPARTMENT OF EMBRYOLOGY. 115 



dedifferentiation, but continue in a progressive development. "WTien 

 the embryo reaches a length of 30 mm. there begins a disproportion 

 in the rate of growth as between the vertebral column and the spinal 

 cord, the former elongating more rapidly than the latter, as may be 

 seen in the accompanying figure. This results in a relative displace- 

 ment of the two, the ventriculus terminalis in the 221 mm. fetus (25 

 weeks) lying 9 segments higher than it did originally and, by the time 

 the adult form is attained, 2 more segments have been added to the 

 displacement. We may say, therefore, that the filum terminale repre- 

 sents that portion of the spinal cord caudal to the second coccygeal 

 segment (thirty-first segment), which has undergone dedifferentiation 

 and has finally become converted into a fibrous strand. This strand, 

 like the sacral nerve-roots, elongates by interstitial growth in adapta- 

 tion to the ascending displacement of the spinal cord. It is of interest 

 to note that the caudal tip of the dural sac maintains its relation to the 

 vertebrae rather than to the spinal cord and remains attached to the 

 filum terminale in the sacral region at a more or less fixed point. 



WTiile in Baltimore, Professor 0. Van der Stricht completed a study 

 of the development of the tunnel space, pillar cells, and the Nuel spaces 

 in the organ of Corti, based upon histological preparations taken from 

 young cats, bats, and common and white rats. This work is, in a way, 

 an extension of that published by Professor Van der Stricht in volume 

 XII of the Contributions to Embryology, and consists of a careful 

 morphological study of these structures, concerning the development 

 of which almost nothing was knowTi. He finds that the tunnel space 

 develops around the spiral nerve-bundle. Originally it is represented 

 by an intercellular cleft, the fluid contents of which are elaborated in 

 the vacuolated cytoplasm of the pillar cells and discharged into the 

 adjoining space. A part of this secreting protoplasm undergoes a 

 process of liquefaction, thus enlarging the cleft and increasing its 

 fluid content. As the cleft enlarges the cytoplasm of the intermediate 

 portion of the pillars decreases through a process of secretion and 

 cytolysis until it is reduced almost to its fibrillar apparatus for support. 

 The author describes in detail the subsequent development of the 

 pillar cells and of their heads. The spaces of Nuel, like the tunnel, 

 arise as intercellular clefts within which is accumulated a fluid dis- 

 charge derived from the cytolysis and liquefaction of the adjacent 

 apparatus. The fluid contents of the tunnel and of the first space of 

 Nuel communicate ^ith those of the second, third, and fourth spaces 

 of Nuel. The contained fluid of all these anastomosing spaces is 

 separated from the otic fluid of the cochlear duct by the thin mem- 

 branous roofs of these interstices. Professor Van der Strict regards this 

 apparatus as designed for the propagation of vibratory waves from the 

 basilar membrane to the tectorial membrane contained in the cochlear 

 canal. 



