PROF. STRASBURGER S OBSERVATIONS ON PROTOPLASM. 127 



sessilis. Under tile action of absolute alcohol the structure 

 bf the ectoplasm became very evident, but the cilia suffered ; 

 w^ith one per cent, solution of chromic acid the structure of 

 the ectoplasm was not clear, but with one per cent, solution 

 of osmic acid, the structure of the ectoplasm was well brought 

 out and most of the cilia remained uninjured. (Figs. 1, 2, 3). 



From these osmic-acid preparations it appears that the 

 ectoplasm contains imbedded within it small rods with re- 

 latively large interstices between them, these interstices being 

 filled with watery protoplasm. Externally and internally 

 these rods come into contact with a very delicate continuous 

 layer of protoplasm, the internal layer not being very clearly 

 defined from the endoplasm in which the chlorophyll-grains 

 are imbedded. 



It appears, further, that the cilia arise from these denser 

 portions of the ectoplasm, each rod bearing a cilium which 

 is more slender than the rod and about twice as long. 



The ectoplasm first appears at the anterior end of the 

 zoogdnidium, and is gradually developed towards the pos- 

 terior end. When it at length invests the whole surface, it 

 is about twice as thick anteriorly as posteriorly. The above 

 mentioned structure can be made out in it at its first ap- 

 pearance. 



In order to follow the development of the cilia. Professor 

 Strasburger made a series of observations upon fresh material, 

 and he found that their formatioi\ followed closely upon the 

 differentiation of the ectoplasm. In the earliest stage the cilia 

 kre small processes of the ectoplasm corresponding in position 

 to the rods at a later stage ; they are somewhat longer ; the 

 full extremity of each being terminated by a knob ; as cle- 

 veloj^ment j^roceeds the cilia become longer and the knobs 

 become smaller in proportion to the increase in length, until 

 the final hair-like form is reached. So long as the zoogoni- 

 dium is in contact with the cellulose wall by which it is 

 surroimded, the cilia are closely appressed to the surface of 

 the ectoplasm, with their apices directed forwards ; it is only 

 when the zoogonidium contracts from the cell- wall that the 

 cilia stand out at right angles to its surface and commence 

 their movements. Professor Strasburger points out that this 

 mode of development of cilia resembles the manner in 

 which the pseudopodia of Rhizopods are formed,^ and he 

 adds that the development of the " bridles " of protoplasm, 

 which occur in the cells of Spirogyra, takes place in the 

 same way. After a longer or a shorter period of activity the 

 cilia are restricted ; a knot begins to be formed at the ex- 

 ' Max Schulize : 'Protoplasm/ n. 24^. 



