APPENDIX 281 



which the filaments are protruded, but this was not seen in the peripheral 

 aggregates of this species, nor at all in the active condition of the other 

 species. 



Labyrinthula is actively parasitic on the algae which it infests, 

 breaking down the contents of the cells into a granular mass. 



As the result of drying, the organism passes into a condition of 

 encystment. The units became closely aggregated and each secretes a cyst- 

 wall, which is double in L. cienkowskii. A firm common envelope may 

 now be formed (in L. macrocystis, Fig. 3 (5), but not in other species) in 

 which the encysted units are embedded. 



The behaviour of the encysted unit appears to vary in the different 

 species. In L. cienkowskii Zopf describes and figures the emergence of a 

 single mass from the cyst. In the other species, Cienkowski found that the 

 contents divided into four within the cyst (Fig. 3 (6 and 7)). Zopf observed 

 the protrusion of one or two long pointed pseudopodia, on hatching, and 

 the final emergence of the protoplasmic mass from the cyst, which was 

 left empty. From the fact that on one occasion three empty cases were 

 found with three units in their neighbourhood, and that these were in 

 connection by their pseudopodia, Zopf concludes that the hatched units 

 join with one another to start a fresh association. 



Zopf regards the association of units of Labyrinthula as representing 

 a stage in the formation of a plasmodium intermediate between the true 

 plasmodium of the Euplasmodida (cf. p. 43), in which there is a complete 

 fusion between the protoplasmic bodies of the uniting amoebulae, and the 

 pseudoplasmodium of the Sorophora, in which the amoebulae, aggregating 

 before spore-formation, come into apposition but maintain their distinct- 

 ness (p. 60). This intermediate form he would distinguish as a Thread- 

 -plasmodium (Fadenplasmodium). 



The propriety of this view seems far from clear. We are familiar 

 with many cases among Protozoa in which an association of individuals, 

 a. colonial organism, is formed by the successive multiplication of the 

 units, whose offspring remain in connection by protoplasmic processes 

 (Colonial Radiolaria, Volvox, Mikrogromio), and the higher animals and 

 plants are often regarded as such colonial organisms, in modified 

 forms. 



That an increase in the number of units in the associations of Laby- 

 rinthula occurs by binary fission of the units is abundantly clear. It is 

 true that it appears probable, from Zopfs observation above quoted, that 

 a fusion may occur in Labyrinthula (though it was not actually observed) 

 between the pseudopodia of individuals recently emerged from the 

 encysted state ; but a parallel to this process may be found in the 

 fusion of the protoplasmic masses emerging from the cysts of the 

 sclerotial condition of the Mycetozoa on revival of activity (cp. p. 50). 

 There are fair grounds for regarding the fusion of the amoebulae 

 by which the Mycetozoan plasmodium takes its origin (in the Euplas- 

 modida) as a part, at any rate the plastogamic part, of a sexual union of 

 which the final, karyogamic, stage is deferred. It would not be sug- 

 gested that the fusion after the sclerotial stage is a repetition of this 

 process in the Mycetozoa, and we may well hesitate, in the present 



