CHAPTER XI 



CHOEDATA 



THIS designation, in its narrower limits, is applied to a 

 group of animals which possesses many structural points 

 that pertain equally to the vertebrates in their embryologi- 

 cal stages, thus forming a connecting link between the 

 two great divisions. 



In its broader sense, and in some of the most recent 

 classifications, it includes the vertebrates. 



Balanoglossus. This animal has long perplexed natura- 

 lists. It is of wormlike form, and by the earlier writers 

 was classed as a worm. 



In the developmental stages of some of its species there 

 are structures which are closely parallel with the larval 

 stages of Echinoderms, so by some authorities Balano- 

 glossus has been ranked as an outlying^di vision of these. 



Not until 1883, when Bateson made an elaborate study 

 of this strange animal, were its affinities with the higher 

 orders discovered. 1 It has many resemblances to the 

 lancelet, and to the embryos of all vertebrates. 



For some time it has formed a division of its own, under 

 the title of Enter opneusta. 



Balanoglossus has a wide geographical range, extending 

 from the Arctic Seas to New Zealand. 



1 Some years prior to this I had, while dissecting some 

 specimens which I had brought from Herm Island, been astonished 

 on finding branchial arches, and corresponded with a scientific 

 friend, Mr C. Davey, B. So., on the matter, but was not sufficiently 

 sure of my ground to make the matter public. 



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