THE GREEN ALGiE 631 



plasm of the cell, and this has been looked upon as a primitive 

 feature. The individuals of Chlorogonium (fig. 1, h) are fusiform, 

 have a thin, closely adherent cell-wall, and a rather ill-defined 

 chloroplast with a considerable number of pyrenoids. Hcemato- 

 coccus {SpJiccrella) is distinguished by the marked separation of 

 the outer portion of the cell-wall from the cell-contents, probably 

 due to the mucilaginous character of the inner layers of the wall ; 

 the space between contents and wall is traversed by branched 

 protoplasmic strands, which have been regarded as pseudopodia 

 by Wille (69), or, perhaps better, as branched pits by Oltmanns 

 (53, p. 141). The genus Brachiomonas (Bohlin 7, West 66), 

 lastly, is interesting owing to its peculiar shape (fig. 1, 1) and 

 to the fact that the daughter-individuals acquire their mature 

 form before they are liberated from the mother-cell (autospore- 

 development). 



In addition to this main series we have two interesting side- 

 lines, the colourless Polytomaceae (Franze 26) and the bivalved 

 Phacotaceae. The former are an almost exact replica of the 

 Chlamydomonadaceae, but lack even the remains of a chloroplast, 

 although large amounts of starch-grains are formed in the cells. 

 The two genera of the order are incompletely known, but 

 Polytoma is like a colourless Chlamydomonas, while Chlamydoble- 

 pharis in its offstanding wall resembles a Hcematococcns. These 

 genera call for comparison with the colourless forms of Euglena, 

 and like these they are no doubt saprophytic degenerates of 

 green ancestors. 



The chief respect in which the Phacotaceae (Dangeard 16 

 and 17) differ from the Chlamydomonadaceae lies in the fact that 

 the coarse wall consists of two halves, which fit together by 

 their thickened rims like two watch-glasses (fig. 1, k). In the 

 formation of daughter-cells the two halves of the wall move 

 apart from one another, but remain connected by mucilage, until 

 the daughter-cells have attained their mature structure. 



Before attempting to trace out the numerous lines of algal 

 descent that emanate from Chlamydomonas and its allies, we 

 may for a moment turn our attention to the Flagellate ancestry 

 of the forms hitherto described. The first genus that calls 

 for notice in this connection is Dangeard's Polyblepharis 

 (Dangeard 16), a unicellular organism, having a simple ovoid 

 shape, closely resembling a Chlamydomonas, but bearing from 

 six to eight cilia, and devoid of a cell-wall (fig. 1, l). The front 



