36 T. H. MORGAN. 



PART IL— THE METAMORPHOSIS OF 

 TANYSTYLUM. 



The material for the second and third parts of the present 

 account was collected during the summer of 1890, while at the 

 Marine Biological Laboratory at Wood's Holl, Mass. I wish to 

 express my gratitude to the Director, Prof. C. O. Whitman, and 

 to the trustees of the laboratory, for the opportunity to carry on 

 investigations under the favorable conditions offered at the 

 marine station. 



My object in giving the figures and description of the meta- 

 morphosis of Tanystylum is, in the first place, because I was 

 fortunate enough to obtain probably a complete series of the 

 larval stages of this Pycnogonid, and inasmuch as the remark- 

 able condition of the development, and adult condition of the 

 appendages of the Pycnogonids, offer in themselves a most interest- 

 ing field for study, I hope a contribution to the complete metamor- 

 phosis of one form may be found useful. Again, by means of 

 serial sections of each of these stages, I hope to have added a 

 little to our knowledge of the internal changes taking place 

 during development, as heretofore we have had only such knowl- 

 edge as could be gained by surface views. Lastly, the figures 

 give a series to which intelligible reference may be made when 

 speaking in Part III of the Development of the Eye. 



ISTot much difficulty was experienced in getting excellent sec- 

 tions of the embryo during its metamorphosis. As described in 

 Part I, the embryos were killed in alcoholic picro-sulphuric 

 solution (35 per cent alcohol saturated with picric acid, to which 

 the usual amount of sulphuric acid was added). Before staining, 

 the appendages were cut off (only possible, however, in the later 

 stages) and the body stained overnight in hasmatoxylin ; after- 

 wards embedded in paraffine and cut into sections, which are 

 better if cut so thick as 10 to 15 p. The figures on Plate V 

 were all drawn to scale, showing the enormous increase of growth 

 during larval life. Figs. XXV and XXVI of Plate VI were 

 also drawn to the same scale. 



I cannot be sure that the series of figures drawn on Plate V 

 and Figs. XIX, XX, XXI on Plate VI give the perfectly com- 



