VEBTEBEATA 



183 



Relations 

 of llcmi- 

 thorda 

 to Verte- 

 brate 

 ancestry. 



sand-life, and possibly to some extent degenerate, yet has 

 not to any large extent fallen from an ancestral eminence. 

 Tho ciliated epidermis, the long Worm-like form, and tlie 

 complete absence of segmentation of the body-muscles lead 



us to forms like the Nemertines. The great proboscis of 

 Balanoglossus may well be compared to the invaginable 

 organ similarly placed in the Nemertines. The collar is 

 the first commencement of a structure destined to assume 

 importance in Cephalochorda and Craniata, and 



great 



perhaps protective of a single gill-slit in /!ti/iiii"t//i>ssus 

 before the number of those apertures had been extended. 

 Borrowing, as we may, the nephridia from the Nemertines, 

 and the lateral in addition to the dorsal nerve, we find 

 that Balanogloews gives the most hopeful hypothetical 

 solution of the pedigree of Vertebrates. Space has not 

 permitted us to go so fully into pros and cons as the 

 speculative nature of the subject requires ; but we give 

 the final conclusion to which our consideration of the 

 structure of the four great branches of the Vertelrata leads 

 in the form of the accompanying genealogical tree. 



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