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THE AMERICAN NATCRALIST. [Vol. XXXVIIl. 



of the protoplasm. It is frequently associated with a plastid. 

 The pigment may be readily broken down and dissolved out by 

 such reagents as alcohol and ether. In chemical composition it 

 is very close to haematochrome and thus may be related to 

 chlorophyll or a derivative of that substance. The cytoplasm 

 around the pigment spot is unthfferentiated and when the color- 

 ing matter is removed it is ver>' difficult and sometimes impos- 

 sible to find the situation of the structure. Consequently the 

 pigment spot can hardly be considered a protoplasmic organ 

 since it is merely an accumulation of coloring matter at some 

 point in the cell. Strasburger (:oo, p. 193) states that the 

 pigment spot of certain zoospores (Cladophora, etc.) is formed 

 in the plasma membrane but this is not true of many other 

 motile cells (Flagellata) and there is no doubt that in some cells 

 {e. g. the gametes of Cutleria) the pigment spot is a portion of 

 a plastid. The literature upon the structure and function of 

 pigment spots is reviewed by Zimmermann {Bcitmgc z. bot. 

 Ccntmlb.Bd. 4, ]i. 159, 1894) and since then Wager ('99) has 

 presented a detailed study of Euglena. 



2. The Sperm. 



The sperm is unquestionably derived from the zoospore 

 through ])rimitive types of gametes which were identical with 

 zoospores in all essentials of morphology. I have described the 

 origin and evolution of sexual cells of plants in tw^o recent 

 papers {Po/^Nlar Scinicc Monthly, Nov. 1901, p. 66 and Feb. 

 1902, p. 300). W e should expect the simplest forms of sperms 

 to have the characters of zoospores and this is the fact. The 

 sperms of the Alga;, as a rule, have the same number of cilia 

 (usually two) as their ancestral asexual zoospores. They gener- 

 ally contain a chromatophore, although sometimes much reduced, 

 and there is present the pigment spot. The cilia are attached 

 at the pointed end or at the side, arising from colorless pro- 

 toplasm that sometimes contains the i)igment spot while the 

 chromatophore, when present, and the nucleus lie at some 

 distance from this region of the cell. The si)erms of bryophytes 

 and pteridophytes are much attenuated in form and lack the 



