i66 ^ NATURAL SCIENCE. march. 



As in all the islands, there is a great difi'erence between windward 

 and leeward sides, the former affording some of the most beautiful 

 scenery and luxuriant vegetation of any seen during the trip. 



Kidney Tubes in Amphioxus. 



Dr. Theodor Boveri, of Munich, has made one of the most 

 striking zoological discoveries of recent times. In Spengel's Zool. 

 Jahvbucher (vol. v., p. 429), he describes and figures a system of seg- 

 mental canals in Amphioxus. These occur all along the region of the 

 pharynx — one pair for each two pairs of gill-slits. They lead from the 

 body-cavity to the atrial sac. There are 90 pairs altogether : the 

 first and the last open by single ciliated funnels into the coelome ; 

 the others by from five to seven funnels. A network of blood- 

 vessels covers the funnels, and Boveri shows that carmine and indigo- 

 carmine taken into the blood reach this network and are removed 

 by the funnels. He gives a series of striking arguments in favour of 

 regarding half the atrial cavity as the homologue of the primitive 

 pronephric duct of Craniata. The whole paper is wonderfully con- 

 vincing ; and one has only to look for a moment at sections of 

 Amphioxus to see the canals, and to be astonished that one has not 

 seen them before. 



To readers who are not specialists in Zoology, the discovery of 

 kidney tubes in Amphioxus may seem a matter of little moment ; but 

 the presence of a definite order and sequence in the development of 

 the excretory organs is one of the strongest links binding together the 

 Chordata — the group of animals which includes the vertebrates and a 

 few lowly forms which have only the gelatinous rod which, in 

 vertebrates, is the embryonic predecessor of the vertebral column. In 

 all the members of this group, the excretory organs first appear as 

 simple tubules, like the tubules of worms. These open at one end by 

 a funnel into the body-cavity ; at the other, into a longitudinal duct 

 at each side. In higher vertebrates, like birds and mammals, a com- 

 plicated series of changes supervenes, and the original excretory organ 

 comes into use as part of the reproductive apparatus while the perma- 

 nent kidney is developed in connection with the posterior end of the 

 original organ. Probably there is no plainer instance of the embryo- 

 logical law that the individual in its development travels along the 

 path its ancestors traversed in their evolution ; for practically every 

 term in the series of changes in the higher vertebrates is preserved as 

 the adult condition in some lower form. It was a puzzle why 

 Amphioxus, which in so many of its organs preserves stages embryonic 

 in higher animals, should be inexplicable in the set of organs most 

 clearly identical in other chordates ; and now Boveri has shown 

 that its excretory organs are precisely what analogy and homology 

 alike demand. 



