158 



MKKISTIC VARIATION. 



[PART i. 



lik<- tin- ^piral valve of an Elasmobranch's intestine.] CoRI, 

 Z.f. w.Z., i. iv. is:i:>. ].. 573, figs. 5, 6 and 7. 



I B 



III 



I'i .. '_'-!. Sjiiral segmentation in Littnbricns terrestris. 



I. A, tin CUM N'>. '.12 ; I. B, diagrammatic representation. 



II. A, the case No. ( ,(3 ; II, B, diagrammatic representation. 



III. tla-c:i*L- No. '.M. i After Com.) 



Two oilier rases described by CORI may be mentioned here, though 

 tin-re is ;i presumption that they are not really examples of Variation 

 in the .segmentation along the axis of a Primary Symmetry, but rather 

 In-long to the class of Secondary Symmetries. They are alluded to 

 liere as it is convenient to illustrate this distinction by taking them 

 in connexion with the examples just given. 



'95. Hermodice carunculata. ( Fig. I'D, III.) Between two normal 

 segments is what seems at first to be a segment double on the left 

 MI!.- with two complete sets of parapodia, but imperfectly divided 

 on the right (left of figure), the septal groove stopping short before 

 it readies the parapodia] region. The lower half on this side is re- 

 pn ented with a normal ventral ramus of ihe parapodium, Imt the 



\entral ramus in the upper was itself 



doubled, having in 



particular two cirri Cv. I. and Cv. II. and two branches of setae. The 

 eonilition of the dorsal ramus is not described. Of course without 

 seeing this specimen it is impossible to say more than this, but the 

 figure strongly suggests that the division between the two halves of 

 thU parapodium was a i/irixion lut,, 'unity* and not into successive 

 aenta. The lignre represents the lower cirrus Cv II. as standing 

 in the normal position for the cirrus, on the posterior limb of the 

 parapodium, hut the .-interior cirrus is distinctly shewn as placed on 

 the anterior limb of the elevation and anterior to the bristles. If 

 this were aetually the rase, this doiiNe parapodium must be looked 

 <>" as a kind of l.ud. with a distim-t Se.-omlary Svmmetry of its 

 own. he.M-rilicd afresh from Com, C. J., Z. /.' </. Z., L1V. 1892, p. 574 



. O * * 



ii-. 3. 



