138 REPORT OF COMMISSIONERS OF INLAND FISHERIES. 



regard this process as consisting of two fused extra dactyls. Inter- 

 preted in this way, it will be seen that we might split this abnormal 

 part in such a way that we would have two extra processes which 

 could be shown to conform to all the criteria in regard to mirror 

 images, relation of the toothed borders, etc., as in the preceding case. 

 Specimens 1 and 2 may, therefore, be regarded as conforming with 

 Bateson's principles for secondary symmetry. And, indeed, the 

 above somewhat elaborate demonstration of this fact would hardly 

 be necessary were it not that it finds its justification as an intro- 

 duction to the following more complicated cases. 



3. Extra Processes Repeating more than One Segment. 



This group includes specimens Nos. 3, 4, 5, and 7. The extra 

 segments for each of these four segments arise from the following 

 morphological surfaces of the appendage; No. 3, from the dorsal 

 surface; No. 4, somewhat ventral to the posterior surface; No. 5 

 slightly dorsal from the direct anterior face: and, finally, in speci- 

 men No. 7, the abnormal structure arises slightly posterior from the 

 ventral surface. The comparison of the actual spatial relations 

 among the elements of these abnormal limbs, with the relations 

 theoretically demanded by Bateson's principles, will be facilitated 

 by the following diagram. (Diagram B.) 



The figures I-V in this diagram represent cross sections of the 

 normal and extra claws taken through homologous points on the 

 dactyls and indices. In each case the smaller section represents the 

 dactyl, and the larger one, the index. As in the preceding diagram, 

 the pointed portion of each cross section indicates the toothed mar- 

 gins of each jaw, and the light and dark areas, respectively, indicate 

 the anterior and posterior surfaces. Fig. I shows a section through 

 the normal dactyl and index of the right chela; the sections in figures 

 II-V represent the extra pair of claws for the specimens about to be 

 described, and show the theoretical relations of these claws corre- 

 sponding to the surface origin given for each specimen. 



