EMBRYOLOGY OF CRYPTOBRANCHUS 457 



gain a fair idea of what is going on inside. The ciliation of the 

 ectoderm of the late embryo, and some features of the circulatory 

 system, are best studied in living material. 



An accurate and complete time record (Section X) of the 

 course of development has been obtained by comparison of many 

 different records of material kept alive during long periods of 

 time; these results were checked by observing the rate of devel- 

 opment of material freshly collected. One lot of embryos, col- 

 lected in the fall of 1906 at the time of the closure of the neural 

 folds, were kept alive in the Zoological Laboratory of the' Univer- 

 sity of Michigan throughout the entire larval period, and their 

 metamorphosis was observed at the end of the second year after 

 fertilization. Specimens were preserved at intervals; shortly 

 after metamorphosis the half-dozen remaining individuals died 

 from causes unknown. Another lot of embryos collected in 

 an advanced gastrula stage in the fall of 1910, were kept alive 

 and in good condition in the Zoological Laboratory of the Univer- 

 sity of Wisconsin until May, 1911, when the last ones were pre- 

 served. 



The study of external and internal structure has gone hand 

 in hand, except for the post-gastrula stages; here, doubtful points 

 in the interpretation of the external structure have in most cases 

 been investigated by reference to serial sections. 



In preparing the illustrations, composite or ideal figures have 

 been avoided. Each drawing, unless otherwise specifically 

 stated, is a faithful representation of an individual embryo; a 

 sufficient variety of figures has been given to illustrate the most 

 important deviations from the condition regarded as typical. 

 All the drawings are the work of the author except figures 268 

 to 276 which were drawn by Prof. Bashford Dean and with his 

 generous permission are here published for the first time; figure 

 203 which was kindly contributed by Dr. L. Hussakoff of the 

 American Museum of Natural History; and figures 277 to 279 

 which were drawn by Miss Hedge of Columbia University. 



The histological technique employed has already been given 

 in Part I; it remains to record the methods used in photography. 

 For embryonic stages, fixation in Solution B (see Part I) followed 



