172 JULIAN S. HUXLEY. 



coelornic habitat, precocious association, and degenerate 

 structure, the reader is referred to Woodcock (6). SuflBce 

 it here to say that the course of affairs in Ganynnedes must 

 have been somewhat different. It is probable that Gany- 

 medes at first associated only at the close of the trophozoite 

 stage. Some of the couples having migrated into the liver, 

 found it (like the coelom for other Monocystidea) a safe 

 retreat and abounding in soluble food. Here too the 

 Gregarine could afford to dispense with all the structures 

 necessary for a life in the open gut, and devote all its 

 energies to growing. One might have thought then that 

 Ganymedes Avould have associated in the sporozoite stage, 

 like Cystobia, and migrated at once into the liver; but, 

 whether non-motile couples below a certain size could be 

 expelled from the tubes or be engulfed and digested by the 

 activity of the liver-cells (see Smith, 5, p. 536), or from some 

 other cause, Ganymedes has found it necessary to remain 

 in the gut till it has attained a definite bulk, thus presenting 

 to us the phenomenon of two sharply-distinct trophic phases 

 after the sporozoite stage. As the parasites are non-motile 

 when they are about to sporulate, conjugation must needs be 

 precocious, so that no Gregarine shall migrate alone into the 

 liver, and thus be, from the point of view of the species, 

 wasted. For this fairly lasting association some special 

 mechanism was impei-ative, hence the cup and ball; while 

 the necessity of remaining some time in the gut has led to 

 Ganymedes retaining more of the original Polycystid 

 structures than is usual in the morphologically degenerate 

 Monocystidea. Finally, although the sporogony remains 

 unknown, it may be confidently prophesied that this Grega- 

 rine will be found to be completely isogamous. 



Thus it will be seen that the Ganymedidae diverged 

 very early from the Monocystid stock, and possess now 

 many new and peculiar charactei-s intermixed with those 

 they have inherited from the common ancestor. For the 

 complete disentangling of these from each other, further 

 work must be done on Ganymedes, and in addition all 



