PROTOPLASM AND LIFE. 739 



acquainted with the further history of the embryo, I would refer to 

 the excellent address delivered two years ago at the Plymouth meet- 

 ing of the Association by one of my predecessors in this chair Pro- 

 fessor Allen Thompson. 



That protoplasm, however, may present a phenomenon the reverse 

 of that in which a simple cell becomes multiplied into many, is shown 

 by a phenomenon already referred to the production of plasmodia in 

 the 3fyxomycetce by the fusion into one another of cells originally 

 distinct. 



The genus Myriothela will afford another example in which the 

 formation of plasmodia becomes introduced into the cycle of develop- 

 ment. The primitive eggs are here, as elsewhere, true cells with nu- 

 cleolated nuclei, but without any boundary membrane. They are 

 formed in considerable numbers, but remain only for a short time 

 separate and distinct. After this they begin to exhibit amoeboid 

 changes of shape, project pseudopodial prolongations which coalesce 

 with those of others in their vicinity, and, finally, a multitude of these 

 primitive ova become fused together into a common plasmodium, in 

 which, as in the simple egg-cell of other animals, the phenomena of 

 development take place. 



In many of the lower plants a very similar coalescence is known to 

 take place between the protoplasmic bodies of separate cells, and con- 

 stitutes the phenomenon of conjugation. 8pirogyra is a genus of 

 algje, consisting of long, green threads common in ponds. Every 

 thread is composed of a series of cylindrical chambers of transparent 

 cellulose placed end to end, each containing a sac of protoplasm with 

 a large quantity of cell-sap, and with a green band of chlorophyl 

 wound spirally on its walls. When the threads have attained their 

 full growth they approach one another in pahs, and lie in close prox- 

 imity, parallel one to the other. A communication is then established 

 by means of short connecting-tubes between the chambers of adjacent 

 filaments, and across the channel thus formed the whole of the proto- 

 plasm of one of the conjugating chambers passes into the cavity of 

 the other, and then immediately fuses with the protoplasm it finds 

 there. The single mass thus formed shapes itself into a solid oval 

 body, known as a " zygospore." This now frees itself from the fila- 

 ment, secretes over its naked surface a new wall of cellulose, and, 

 when placed in the conditions necessary for its development, attaches 

 itself by one end, and then, by repeated acts of cell-division, grows 

 into a many-celled filament like those in which it originated. 



The formation of plasmodia, regarded as a coalescence and abso- 

 lute fusion into one another of separate, naked masses of protoplasm, 

 is a phenomenon of great significance. It is highly probable that, 

 notwithstanding the complete loss of individuality in the combining 

 elements, such differences as may have been present in these will al- 

 ways find themselves expressed in the properties of the resulting plas- 



