5 34 JOHNSON. [Vol. V III. 



normal form. A striking fact in the history of Balbiani's 

 monster is its fission previous to the disappearance of its bifid 

 structure, which it therefore transmits to its proximal offspring. 

 There was, however, not the slightest development of duality 

 in the distal offspring ; even in the proximal it quickly 

 disappeared, and the normal form was regained. 



In the light of Balbiani's most recent experiments upon 

 Stentor ('92), I am led to believe that double monsters of this 

 species, and doubtless of Infusoria in general, owe their origin 

 to the temporary dualism of the cytosome at time of fission. 

 If through imperfect development or mutilation the normal 

 progress of fission is interfered with, the dualism already set up 

 in the cytoplasm does not fail to manifest itself in the pro- 

 duction of a double monster. Some of Balbiani's figures 

 (especially Fig. /b^-bS, PI. II, '92), show the gradations 

 between a nearly-divided merozoan (originally cut from a 

 Stentor in fission), and a perfect double monster with two 

 frontal fields. 



The duplication of newly-formed organs in both zooids in 

 fission is another interesting instance of dualism, comparable 

 to the simultaneous appearance of new zones in a double 

 monster. It was observed by Stein ('67) and carefully studied 

 by Sterki ('78) in the neoformation of marginal cilia and of 

 cirri in both daughter-individuals of Stylonichia.^ 



The position taken by the meganuclei in a double monster is 

 worthy of notice. A nucleus is usually present in each moiety 



1 The regeneration of ciliary organs in the Oxytrichina is of especial interest. 

 These organs, as is well-known, are highly differentiated, occurring in form of 

 cirri, spines, etc., which are definite in number. In regard to their development, 

 the work of Stein and of Sterki has shown that the frontal, ventral, and 

 anal cirri by no means originate in their definitive form and position. Their 

 earliest appearance as a group of six parallel rows of minute, similar processes, 

 from which the cirri develop and are shifted to their final positions, is very 

 suggestive of the primitive six rows of cilia of the lower Ilypotricha {e. g., 

 Urostyla). The point of chief interest in this connection is, that new cirri are 

 formed, not alone for the posterior zooid, but also for the anterior, where the old 

 frontal and ventral cirri atrophy and are replaced by the new ones. In the 

 posterior zooid, on the other hand, the caudal cirri of the parent are replaced by 

 the newly-formed cirri. Just as in Stentor, the neoformation of a structure 

 demands the atrophy of its preexisting homologue. 



