KONGL. SV. VET. AKADEMIENS HANDLINOAR. HAND 25. N:() 9. 7 



It must, however, he borne in niiiul, that tlic smallest embryo segments not always 

 give rise to a dimorphous colony, but at once assume the mature arrangement of the 

 segments. Such forms are often apt to a pygmean growth. The same mode of evolution 

 in other genera, particularly in Milioliua, has been made the object of most painstaking 

 researches by the experienced Rhizopodologist M. Schlumbekger, who with the utmost 

 skill and sedulity, in numerous papers' — mostly during the last seven years published in 

 the Memoires and Bulletins de la Societe Zoologique de France and in Memoires de la 

 Socicte geologique de France — has produced masses of examples of this evolutional pro- 

 cess in some Miliolina3. In these excellent expositions it is stated, that the smallest prim- 

 ordial segments give rise to a larval stage generally of (jumi/'iu'lncul/ni' arrangement of 

 the segments, often succeeded by a trilocidini' development, \vhereupon follows the ma- 

 ture biloculine condition. 



Instances of a total triloculine larval stage will also be met with, being a shorter 

 step to the fully developed hilocidine stage. The initial segment in such forms is gene- 

 rally somewhat larger than in the last mentioned forms. 



As in the instances of polymorphism in Frondicularia the differences in the arran- 

 gement and number of segments in the larval stage are subject to great variation, so may 

 also the polymorphism in the Miliolinm be looked upon as vacillating gradations of 

 evolution, which cannot aft'ord satisfactory distinctions for establishing species; and that so 

 much the less, when we consider, that initial segments with different power of growth are> 

 as stated above, produced by one and the same individual segment. An arrangement of 

 the larval segments may in several instances appear as being directed by a clear mathe- 

 matical rule, but which at another time will be eclipsed by irregularities and exceptions. ^ 



To show how little attention has been paid to these facts even by reputed Rhizo- 

 podologists I will reproduce some of v. Reuss' designations amongst an assemblage of 

 Nodosarina communis d'Orb, with varieties, depicted by v. Sciilicht in his valuable me- 

 moir, the Foraminiferen des Septarienthones von Pietzpuhl 1870 (Wien Ak. S. Ber. 62, p. 45.5). 



To any one experienced in dealing with this category of organic forms it will be 

 obvious, that all the forms here (Fig. II) represented fromiig. 1 to fig. 22 must be grouped 

 under Nodos. communis d'Orb. var. consob)ina d'Orb. (a denomination, which will be better 

 substituted by "imupcrata'' d'Orb. the nomen ti'iviale "consohrina" being superfluous). As 

 usually the segments of the more developed stages become more or less inflated and 

 present constricted sutures. 



Fig. 23 — 26 represent forms approaching jVod. Bouecina, ovicida d'Orb. and per- 

 haps the allied farchnen Sold, but may also be considered as a feeble form of the jjreceding. 



Fig. 27 — 34 are forms of A^. communis d'Orb. and not distinct from Nod. Roemeri 

 and mucronata Neugeb. 



' For the courteous commuuicatinn of his memoirs 1 hiive to acknowledge m_v great obligations to 

 the anther. Valuable informations and suggestions on this subject have also been advanced by Van den Brorck 

 in Bull. R. Soc. Malac. Beige (1893), 28: and in Bull. Soc. Beige Geol. (1803), 7. For transmission of his 

 able papers I stand under great obligation fo this author. 



- For a fuller account of the "iliniorphism" see my paper '■Oni den sa kallade verkliga dianiortismen bos 

 Rhizopoda reticulata" 188!), Bib. till K. Sv. Vet. Ak. Ilandl. 15. 4, No. 2. 



