ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 221 



of much interest. Apart from other structural modifications, we can 

 at once point to their monoderic stratum corneum. 



Ciliated Cells.* — How are the cilia of ciliated cells related to the 

 neighbouring parts of the cell ? By a fresh series of delicate obser- 

 vations, Prof. T. W. Engelmann has thrown further light on this 

 question. A highly differentiated cilium with its appurtenances 

 displays under favourable circumstances the following constituents : — ■ 

 There is, first, an intracellular fibre (Wurzelfaser, Wimperwujzel) 

 whose outward end is connected with (2) the pedicle (Fusstiick) of the 

 cilium : this pedicle is separated by (3) an intermediate segment 

 (Zwischenglied) from the cilium proper, resolvable into (4) a proximal 

 hulb and (5) a terminal shaft. _ 



That the intracellular fibres really exist and are not folds of a 

 membrane or otherwise due to optical illusion, can now be demon- 

 strated. They are best seen in cells of the intestinal epithelium of 

 lamellibranchs (Cyclas, Anodon). They traverse the soft substance 

 of the protoplasm, pursuing a parallel course through its outer portion 

 and converging more deeply to form a conical bundle, from whose apex 

 proceeds one long originating fibre (Stammfaser) which thins out so 

 as to be no longer measurable until its pointed end disappears. 

 Although this trunk-fibre may approach or run close beside the 

 nucleus, there is no reason for supposing that it imites with it. The 

 convergence of the fibres is in some cells less marked, and the presence 

 of a trunk-fibre is then doubtful. In others, again, a trunk-fibre 

 seems absent ; here the fibres do not converge, but remain quite 

 parallel to one another, while the inner extremity of each fades away 

 into the surrounding protoplasm. When the fibres are numerous, the 

 protoplasmic interspaces which separate them, near the outer portion 

 of the cell, are about equal in diameter to the fibres themselves, or less 

 than • 3 /x. The separate fibres are smooth or but slightly varicose ; 

 yet they sometimes become very regularly granulated under the in- 

 fluence of reagents or even spontaneously, in the act of dying. Under 

 high amplification each fibre remains homogeneous. Nussbaum was 

 certainly wrong when he viewed the intracellular fibres of the intes- 

 tinal epithelium of Anodon as made up of two apposed anatomical 

 elements, the one elastic and strongly refracting, the other contractile 

 and nearly identical with the adjoining substance of the cell. By 

 using solution of bichromate of potash (4 per cent.) or common salt 

 (10 per cent.), Engelmann, after careful teasing with fine needles, was 

 able to separate en hloc from the rest of the cell the entire fibrous ap- 

 paratus of the cells in question. Such aggregates or quite isolated 

 fibres, the result either of art or accident, serve well to display the 

 connection of the fibres with their corresponding cilia and pedicles. 

 Engelmann also figures very clearly in loco the intracellular fibres of 

 the long cylindrical cells of the gut of Cyclas. These cells, with their 

 fibres and cilia exceptionally conspicuous and few in number, remind 

 us of caliciform secreting cells ; they, indeed, represent an intermediate 

 phase between these and ordinary cells. 



* Pfliiger's Arch. Physiol., sxiii. (18S0) pp. 50.5-35 (1 pi.). 

 Ser. 2.— Vol. I. R 



