276 



FINE-STRUCTURE OF PROTOPLASM 



II 



They are of the same order of size as bacterial cilia and, like them, 

 can only be made visible under the light microscope by methods 

 which increase their width, for example, by the use of an apposition 

 stain. They are also described for aquatic fungi, certain brown flagel- 

 lates (Chrysophyceae) and the zoospores of the Heterocontae among 

 algae. 



In the electron microscope these hairs are very conspicuous (Brown, 

 1945; Foster and co-workers, 1947; Houwink, 195 i). Manton and 

 Clarke (1950) have discovered that the longer one of the two flagella 

 of the spermatozoa of Fucus is also hairy. 



It will be an interesting task to find out whether these hairs are 

 active, like the bacterial cilia, or whether they are passive microfibrils 

 split off the fibrous flagellum in order to increase its propulsive power. 



b. Eggs 



There is a wealth of information on the birefringence of the cortex 

 (Fig. 138) of the sea-urchin egg (Monroy, 1945; Monroy and Mon- 

 talenti, 1947), indicating that this layer is a lipo-protein system 



Fig. 138. Tubifex egg (from Lehmann, 1947). 



(Ohman, 1945). After fertilization, the double refraction disappears 

 for 15-20 minutes, indicating an activation of the cortical layer by 

 temporary hydration and disorientation. Similar structural changes 



