166 ROTATORIA 



Ariuraea Z'olga Ehrenherg (1834) maybe regarded as typically represented by Ebren- 

 berg's best figure (1838, T. LXII, fig. xv, 1), which shows a form in which the posterior 

 width of the lorica is distinctly narrower than the anterior. The right spine is alx)ut one- 

 third, the left one-quarter of the length of the lorica. Reticulate and punctate sculpture are 

 1)1 >th clearly indicated. 



In examining as much material and as many illustrations as are available to us we have 

 rarely had any difficulty in assigning individuals or illustrations to one or the other species. 

 It is true that in a few figures of European specimens (e.g. Virieux 1916, fig. 46, Wesenberg- 

 Lunil, 1930, Plate VH, figs. 8, 26, and 46) the aiitcrinr and posterior borders are equal 

 or the former very slightly longer than the latter. But such specimens do not apjiear to 

 show the pronounced narrowing of z'alga and it must be remembered that a very minute 

 error in drawing on the part of an observer not studying the dimensions in question would 

 produce just such differences as found in some of these figures. Fadeev (1927) used the 

 relation between the anterior and posterior widths of the lorica to separate tropica Apstein 

 from the other forms of K. qiiadrata (s. lat.), apparently understanding b}' Apstein's name 

 what we here regard as K. ralga. Within these species the use of misapplied varietal terms 

 appears to have led to considerable confusion. Thus in his monumental work on the cyclical 

 phenomena in rotifers Wesenberg-Lund (1930) objects to certain of Hartmann's conclusions 

 as to the production of nalga forms from resting eggs. But it is clear from a study of 

 Wesenberg-Lund's figures that what this author calls 7'alga is a form of qiiadrata (s. s.) 

 while Hartmann's observations on this point referred primarily to the true /v. t'a/T'a (Ehren- 

 berg). Since such confusion is bound to result from the present unsatisfactory state of 

 the varietal nomenclature of these two species we have attempted to standardise as far as 

 possible the names of the various forms, introducing a minimum of new names and adhering 

 to the principle of priority. Though the latter is not binding in such cases, it would ajipear 

 to provide the best method of determining the relative merits of two synonyms, and the 

 neglect of the princijjle in the past has led authors to create new varietal names without 

 an adequate study of the literature so that the form of 7'alga with a single posterior spine 

 has been provided with at least three and probably four names. 



Kcratclla qiiadrata (Miiller). 



Kratzschmar (1908, 1913), Hartniann (1918) and Wesenberg-Lund (1930) have 

 studied the morphological cycle in this species. Normally the first generations from se.xual 

 eggs are composed of forms with long divergent spines (f. diz'crgcns Voigt) ; these later give 

 place to forms with shorter more parallel spines (f. qiiadrata Miiller). Later one (f. 

 valgoides n.) or both spines (f. curvicornis Ehrenberg) are lost and at such periods sexual 

 reproduction is stated to occur. The amount of cyclomorphosis is very variable in different 

 localities but in general this species exhibits a cycle of reduction. In a few cases an initial 

 elongation of the spines has been observed and in a series called by Hartmann "A. aculcata- 

 valga," but consisting of apparently morphologically normal reduced forms of K. qiiadrata, 

 the cycle begins with ciiri'icornis, to which the addition of one minute papilliform spine pro- 

 duces the form named by Jakubski (1915) irregularis, and two minute spines tcsludo 

 Ehrenberg. 



In general the two posterior spines of qiiadrata are subequal in length, but in certain 

 forms unequal spines apparently indicate a transition from diz'crgens (right spine) to qiiadrata 

 (left spine). Fadeev has figured as valga a specimen of qiiadrata with unequal subparallel 



