284 THE PHENOMENON OF 



through double conjugation of the contents of two 

 dehiscing mother-cells, which extrude their contents. 

 The conjugation-cell formed in either of these ways, is 

 either itself a reproductive-cell, or the latter is formed by 

 a further metamorphosis of the combined contents within 

 the conjugation-cell, and this mostly takes place either in 

 one of the halves of this, or in the connecting piece 

 between the halves ; it is mostly a resting spore, more 

 rarely an active gonidium, rarest of all the combined 

 contents divide into a number of cells in their transforma- 

 tion for the purpose of fructification. These, and other 

 less essential differences, produce the multiformity of 

 cases in which the phenomenon of conjugation presents 

 itself, especially in certain families of the Algse, while as 

 yet it has only been observed in one genus of the Fungi, 

 here, however, in a modification deviating from all the 

 rest. In the following summary I shall endeavour, 

 as far as possible, to place all the known examples. 



A. CONJUGATION OF SIMILAR CELLS. The uniting cells 

 may be either free and isolated, as in most Diatom aceae 

 and Desmidiaceae, or they may be links of a many-celled 

 filament, as in the Zygnemacese. In isolated cells the 

 Union mostly takes place by the sides of the cells, either 

 by parallel or by crossed approximation (copulatio 

 later alis par allela, s. decussata) very rarely by the apices 

 of the cells (copulatio apicalis). In the jointed (many- 

 celled) filaments the union takes place either by each two 

 successive cells of the same filament anastomosing with 

 their adjacent ends by lateral processes, which we will call 

 chain-union (copulatio catenativa] or by the links of two 

 different filaments (or, as may equally happen, different 

 parts of the same filament overlying through bending), 

 uniting by their sides : yoke-union (copulatio conjugativa\ 

 in which case the cells may be either bent like a knee in 

 order to reach each other (conjugatio genuflexd], or be 

 united without bending, by processes growing out to 

 meet each other and coalescing into a transverse canal : 

 ladder-like union (copulatio scalaris). These distinctions, 



