THE GROWTH AND METAMORPHOSIS OF 

 TORNARIA. 



T. H. MORGAN. 



Balanoglossus, and its larval form Tornaria, seems to occupy 

 a more or less central point in the family tree of the Triplob- 

 bastica. The adult worm is related to all appearances, on the 

 one side, to the vertebrates ; on the other, through such a form 

 as Cephalodiscus, possibly to Rhabdopleura, Polyzoa, and Phronis. 

 The larval Tornaria has characteristics which are supposed to 

 indicate a relationship to the Echinoderms, or even, it has been 

 suggested, to the Trochophore of Annelids. Few animals 

 present so many possibilities to the morphologist. 



The growth and metamorphosis of Tornaria have not been 

 thoroughly studied by the modern methods of technique ; and 

 the following is an attempt to partially fill up this gap in our 

 knowledge of the group. 



The material was collected at Wood's Holl, Mass., while 

 enjoying the opportunities of The Marine Laboratory. I desire 

 to express my obligations to the director, Professor C. O. Whit- 

 man, and to the trustees, for the privilege of studying at the 

 station. 



During August (1890), Tornaria were at times very abundant. 

 When the surface of the water was calm they were caught in 

 the tow-net at flood tide, during both the day and night. Great 

 difficulty was experienced in keeping the Tornaria for any length 

 of time during the period of metamorphosis. Many developed 

 abnormally ; and the oldest one was kept only seventy hours 

 after it had been put into the aquaria. The Tornaria belonged, 

 undoubtedly, to the same species described by Alexander Agassiz 

 in his important paper on Balanoglossus and Tornaria (1873). 

 He referred this Tornaria to Balanoglossus Koivalevski, which 

 is the common form of the New England coast. Bateson, in 

 1884, working on the young of B. Kowalevski, found in the 

 Chesapeake Bay, showed clearly that it had a direct develop- 



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