880 THE ANIMAL KINGDOM. 



shape, a difference which probably does not obtain in Collosphaera and 

 its allies. In the formation of isospores the nuclei, which are doubly 

 refractile, and become more and more so, are scattered through the cap- 

 sular protoplasm ; they multiply by binary fission. Small crystalloids 

 make their appearance, one for each spore, even before the required 

 number of nuclei is attained. The oil of the oil-globule is dispersed as 

 minute granules, some of which are destined for each spore. The pro- 

 toplasm is resolved into as many portions as there are crystals. The ripe 

 isospore is pointed anteriorly, rounded posteriorly. Two flagella spring 

 from the point. The nucleus is large and anterior ; the crystalloid with 

 oil-granules posterior. The formation of anisospores in Collozoum and 

 Sphderozoum contrasts with the above (i) in the grouping of 2-3 nuclei 

 together, and the more refractile and homogeneous character of the 

 protoplasm directly inclosing each group ; (2) in the multiplication of 

 the nuclei in each group and an increase of size in the corresponding mass 

 of protoplasm ; (3) in the differentiation of a nuclear chromatin network ; 

 and (4) the formation of a group of oil-drops in each mass, whilst the 

 central oil-globule dwindles, the oil-drops increasing in number pari passu 

 with the nuclei, but being ultimately dispersed in granules. The ripe 

 anisospore is bean-shaped ; it may or may not contain a minute cry- 

 stalloid ; whether it has a single or double flagellum is uncertain. It is 

 of two sizes ; a large, the macrospore, with a fine chromatin network in 

 the nucleus, and a small, the microspore, one half less in all dimensions, 

 with a coarse chromatin network. Both forms of spores occur in the same 

 central capsule. It has been suggested that they are sexually differ- 

 entiated, but copulation has not been observed. If the suggestion is true 

 and if the isospores are regarded as asexual, then there is Alternation 

 of Generations. In Collosphaera and its allies a corresponding state is 

 evidenced by the transient grouping of nuclei, which however become 

 scattered and then differentiated into macrosporal and microsporal nuclei 

 (supra), the two kinds however in different central capsules. Crystalloids 

 are also always present. The changes undergone during sporulation 

 by the extracapsular region of the body are the disappearance of the 

 vacuoles, the dwindling and softening of the jelly, the aggregation of the 

 capsules in the centre of the colony, the retraction of the pseudopodia and 

 sarcoplegma, and the sinking of the colony in the water. The capsular 

 membrane appears to be resolved and the spores escape. Then the remains 

 of the protoplasm break up into smaller and smaller portions which shrink 

 into brown globules and disperse. The spores of Acantharia are small 

 and pyriform ; with several, probably three, flagella, two at one spot, and 

 one vis-a-vis to it ; a crystalloid may or may not be present * (Brandt). 



1 The flagella of the spores are exceedingly difficult to see. It must remain doubtful for the 

 present whether or no there is any instance of a single flagellum only. The life-history of the 



