960 



SCIENCE. 



[N. S. Vol. IY. No. 104. 



and Field are in error when they aflSrm that the 

 elastica is pierced by cells from the skeletog- 

 enous layer. What they claim as the elastica 

 is not such. The intervertebral ring of carti- 

 lage seems to be formed of the fused inter- 

 calated cartilages, just as in Lepidosteus, and as 

 in this fish becomes cross-segmented to form 

 the articular ends of the adjacent vertebrse. 



A paper* by Dr. H. C. Bumpus, giving results 

 of a study on meristic and homceotic variation in 

 the vertebral axis in Necturus, was briefly re- 

 ferred to by Professor Whitman. 



The scope of the paper and method of deal- 

 ing with the subject will be seen in the follow- 

 ing questions raised and answered more or less 

 fully by the author : 



1. The per cent, of variation in the attach- 

 ment of the pelvic arch. Is there meristic vari- 

 ation and is homoeotic variation associated with 

 it? 



2. Is there a ratio between the absolute 

 length of the animal and the number of verte- 

 brae? 



3. Why does the variation tend towards for- 

 ward rather than backward homoeosis ? 



4. Occurrence of oblique or unsymmetrical 

 sacra. 



5. Is the position of the pelvic arch de- 

 pendent on the ordinal position of some one 

 segment (sacrum), or is it determined by the 

 location of some topographical point ? 



6. Are there variations in the position of the 

 pectoral arch ? and are these correlated with 

 variations in the pelvic arch ? 



7. Are there other skeletal variations asso- 

 ciated with pelvic variations ? 



8. Are variations more frequent in males 

 than in females ? 



9. Are there anatomical grounds for the the- 

 ory of vertebral intercalation ? 



These questions and many others raised in 

 connection with them are answered by the con- 

 ditions presented in one hundred specimens of 

 Necturus. 



Dr. Bumpus has used the expressions ' for- 

 ivard ' and * backward homoeosis ' as defined by 

 Bateson (' Materials for the Study of Variation,' 

 p. 111). 



The pelvic arch is attached in the majority of 



* Soon to appear in the Journal of Morphology. 



cases to the XIX. vertebra. The variation in 

 position in most cases consists in attachment to 

 the XX. vertebra, and this is called forward hom- 

 oeosis. The term ' homoeosis ' is an old one, and 

 Bateson employs it in its strict etymological 

 sense. It is not the term, but the method of de- 

 fining direction, that is open to serious objection. 

 It is decidedly confusing and contrary to general 

 usage to speak of the direction of variation as 

 forward when the homoeosis is exhibited in 

 vertebrse lying behind the starting point. Ac- 

 cording to Bateson' s definition, if the pelvic 

 arch in Necturus were found as far back of the 

 normal position as the last caudal vertebra it 

 would still be a case of forward homoeosis. If 

 the homoeosis appeared in successive vertebrae, 

 coming at each step nearer the caudal end, we 

 should still have to defy common sense and call 

 it ' forward. ' Proceeding in this wise, we 

 should have to speak of the formation of seg- 

 ments in an embryo as progressing forward, 

 notwithstanding that we know that the devel- 

 opment advances in just the opposite direction. 

 From this point of view, the direction of devel- 

 opmental differentiation in general would be 

 forward instead of backward. 



' ' The development of petals in the form of 

 sepals," as Bateson himself suggests, would be 

 ' ' an outward homoeosis, while the formation of 

 sepaloid petals would thus be called an inward 

 homoeosis, and so forth." 



Is anything gained, except confusion, by 

 adopting such terminology? 



Bateson attempts to justify his position in the 

 following words : 



' ' In describing cases of such transformation 

 in the series, it is usual to speak of struc- 

 tures, the pelvis for example, as ' travelling for- 

 ward,' or ' travelling backward.' These modes 

 of expression are to be avoided as introducing 

 a false and confusing metaphor into the subject, 

 for there is of course no movement of parts in 

 either direction, and the natural process takes 

 place by a development of certain segments in 

 the likeness of structures, which in the type 

 occupy a different ordinal position in the series. 

 In using the expression, homoeosis, we may in 

 part avoid this confusion, and we may speak of 

 the variation as occurring from before backward or 

 from behind forwards, according as the segment to 



