THE CENTROSOME AND THE BLEPHAROPLAST 83 



definite functions in the life of the cell. The question of centrosomes in 

 the spermatogenous cells of bryophytes, pteridophytes, and gymnosperms 

 is dealt with in the following discussion of the blepharoplast. 



THE BLEPHAROPLAST 



Occurrence. The blepharoplast, as indicated by the name given to 

 it by Webber (1897), is the cilia-bearing organ of the cell. Blepharo- 

 plasts of one kind or another are found generally in the motile cells of 

 plants and animals, such as motile unicellular organisms (Flagellata, 

 Ciliata, etc.), swarm spores, spermatozoa, and spermatozoids; and also 

 in cells which, though not freely motile themselves, have motile organs 

 performing other functions, as in the case of ciliated epithelium. In 

 plants blepharoplasts are most conspicuously displayed in the sperma- 

 togenous cells of bryophytes, pteridophytes, and gymnosperms (cycads 

 and Ginkgo), where their striking resemblance to ordinary centrosomes 

 has led to much controversy over their nature. Some cytologists have 

 regarded the blepharoplast as a more or less modified centrosome, where- 

 as others have contended that it is a special kinoplasmic or cytoplasmic 

 organ distinct from the centrosome. In recent years the evidence has 

 tended strongly to support the former view. 



In the following pages the blepharoplasts of various organisms and 

 the manner in which they function in the development of the motor 

 apparatus will be described in some detail. Attention will be given 

 chiefly to the situations found in plants; the corresponding phenomena 

 in animals will be more briefly considered. 



Flagellates. In the flagellates several types of flagellar apparatus 

 are found (see Minchin 1912, pp. 82 ff ., 262-3) : in one series of forms 

 the cell contains a single nucleus and "centriole," the latter functioning 

 both as a centrosome and as a blepharoplast. The centriole may lie 

 either against or within the nucleus, so that the flagellum which grows 

 from it appears to arise directly from the nucleus (Mastigind); in other 

 forms (Mastigella) the centriole is quite independent of the nucleus. 



In a second series of forms a single nucleus and centrosome are present, 

 and in addition one or more blepharoplasts. * Three conditions have been 

 distinguished here: (a) at the time of cell-division the blepharoplasts 

 and flagella are lost, new blepharoplasts arising from the centrosomes 

 during or after mitosis; (6) the blepharoplasts may persist, dividing to 

 form daughter blepharoplasts from which new flagella arise (Polytomella) ; 

 (c) the centrosome divides to furnish a blepharoplast which subdivides to 

 two: a distal blepharoplast or basal granule of the flagellum, and a 

 proximal blepharoplast or "anchoring granule" at the surface of the 

 nucleus, the two being connected by a delicate strand known as the 

 rhizoplast, rhizonema, or centrodesmose (Peranema trichophorum) . Entz 

 (1918) has recently reinvestigated the structure of Polytoma uvella, first 



