THE MYCETOZOA 149 



exami^le of social organisation, and it is doubtless advantageous to 

 the species in that often for competition between numerous small 

 and weak plasmodia, each of which might be too small to fruit, 

 there is substituted co-operation which leads to the formation of 

 a vigorous plasmodium large enough to produce one or more fruit- 

 bodies of the size characteristic for the species. 



It has been observed by Jahn ^ that, in the Mycetozoa, e.g. 

 Didymium squamulosum, a zygote, after beginning to feed as a 

 Plasmodium, is able to ingest an unpaired amoebula into a large 

 digestive vacuole and there dissolve and absorb it. This 

 cannibalism, while causing the extermination of useless amoebulae, 

 provides a source of food for zygotes which, after feeding in the 

 usual way on bacteria, etc., may grow into large fruiting plasmodia. 

 Since it has to do with the action of one member of a species on 

 another with some advantage resulting to the species as a whole, it 

 may perhaps be regarded as a social act. The destruction of useless 

 drones in a bee-hive by the worker bees after the marriage of the 

 queen is somewhat analogous from the social point of view, 

 for it, too, leads to a reduction in the number of associated 

 individuals with an ensuing advantage in respect to the food 

 supply. 



In the fruit-bodies of Trichia decipiens, Hemitrichia abietina, 

 H. clavata, etc., and most species of Arcyria, e.g. Arcyria pomi- 

 formis (Fig. 83), certain spores, namely those in the sporangium, 

 become disseminated by the wind and have a reproductive function. 



Fig. 81. — Chondromyces crocatus, one of the Myxobacteriaceae, which exhibits 

 social organisation in the formation of its fruiting structures. Nos. 1-6, succes- 

 sive conditions of cyst formation shown by as many individual colonies. No. 1 : 

 a, a mass of rods just lising from the substratum and becoming constricted at 

 the base ; b, a smaller mass which has begun to secrete a cystophore and has 

 become two-lobed preparatory to branching. No. 2, a more advanced mass, 

 preparing to produce three branches. Nos. 3 and 4, nearly mature cystophores 

 showing branching of the third and fourth order, the ultimate masses beginning in 

 some instances (o a) to bud out into cysts. No. 5, a specimen cultivated on 

 moist agar, the cystophore unusually stout, the ultimate masses almost wholly 

 converted into immature cysts. No. 6, a specimen grown on straw showing 

 normal habit ; the cysts are not yet mature. From a drawing kindly lent by 

 Roland Thaxter ; the same as Plate XXI in Vol. XVII of the Botanical Gazette. 

 The cystophores have an average height of • 6 mm. and rarely attain 1 mm. 



^ Vide G. Lister, loc. cit. Her Fig. 3 which shows zygotes containing ingested 

 amoebulae was drawn from stained preparations lent by Dr. Jahn. 



