GLANDULAR HAIRS OF THE COMMON TEASEL. 169 



this was the case. A drawing is given in fig. 7 of the floor 

 of the segmentation cavity in an unincubated but normal 

 egg, showing nuclei distributed more or less throughout this 

 layer. In some blastoderms incubated as long as sixteen 

 or eighteen hours, the subgerminal layer was very much 

 reduced in size, and in some cases no longer formed a con- 

 tinuous layer, the white yolk projecting between the seg- 

 ments of the subgerminal layer and assisting to form the 

 floor of the segmentation cavity. Nuclei could be detected 

 in these detached portions of the subgerminal layer in some 

 cases. This would seem to show that the subgerminal layer 

 continues to play an important part in development for some 

 time after incubation has commenced. I am not able to 

 state accurately how long the subgerminal layer persists and 

 can be recognised after incubation has commenced. 



These investigations were conducted under the direction of 

 Dr. Klein. 



On the Protrusion of Protoplasmic Filaments from the 

 Glandular Hairs of the Common Teasel {Dipsacus 

 sylvestris). By Francis Darwin, M.B. (Abstract of a 

 paper read before the Royal Society on February 28th.) 



The protoplasmic structures described in the following 

 communication are connected with the glandular hairs or 

 trichomes found on both surfaces of the leaf of the common 

 teasel, Dipsacus sylvestris. The trichomes are of two kinds, 

 differing in a marked manner and shape. The form of 

 gland from which alone the protoplasmic filaments issue is 

 shown in the diagram. The gland consists of a multicellular 

 pear-shaped head, supported on a cylindrical unicellular stalk 

 which rests on a projecting epidermic cell. The whole struc- 

 ture projects about ^ of a millimeter {-^-j-o inch) above the 

 surface of the leaf. 



The filaments issue from inside the gland-cells, reaching 

 the surrounding medium by passing through the external 

 cell- wall of the gland. The point where protrusion takes 

 place is on the summit of the gland, and usually at the point 

 of junction of several radiating cells on the summit of its 

 dome-like surface. The act of protrusion is rapidly effected ; 

 a previously naked gland may be seen to send forth a minute 

 thread of trembling protoplasm, projecting from its summit 

 freely into the surrounding water. The filament grows by 



