ON PTYOHODERA FLAVA. 177 



has given of the other two described species of the sub-genus 

 Chlamydothorax was based in each case on a single specimen 

 preserved in spirit, so that an Enteropueust with an eminently 

 free pharynx has never been studied in the living condition 

 before. And this makes a difference. 



The conclusions arrived at by Spengel, based as they were 

 upon such laborious and prolonged researches, are entitled to 

 the profoundest respect. Still, with the best will in the world, 

 I cannot follow him in his adverse criticism of the theory as 

 to the relationship of the Enteropneusta to the Chordata. One 

 might conceivably be able to relinquish the idea of the existence 

 of a notochord or its representative in the Enteropneusta, but 

 the gill-clefts are a perpetual fact, and it seems little less than 

 perverse not to recognise it. 



Indeed, in his remarks directed against the assumed Chor- 

 date affinities of Balanoglossus, it would almost appear that 

 Spengel has carried the analytical method of argumentation 

 to an extreme, and that he is unable to see a general corre- 

 spondence or homology through the veil of differences in detail. 

 The other extreme is to imagine correspondences where none 

 exist. But it is certainly not necessary to force matters in 

 any way in order to clearly recognise an affinity between the 

 Enteropneusta and the Chordata. 



Unfortunately we are here in the presence of one of those 

 distressing instances, so common in the realm of morphology, 

 in which two entirely opposed views can be more or less equally 

 supported. This is due, as Spengel himself points out (loc. 

 cit., p. 722), to the lack of a definite method or criterion in 

 attempting to answer morphological questions. 



There is, however, a principle which should be of service in 

 this connection, namely, the principle of correlation between 

 structural and topographical features on the one hand, and 

 physiological or functional peculiarities on the other. 



Spengel lays great stress upon the dorsal position of the 

 gill-pores in the Enteropneusta and their ventral (sic) position 

 in Amphioxus, this difference in position being especially in- 

 dicated by the relations of the vascular system, the propelling 



VOL. 40, PART^l. NEW SEE. JJ 



