DEPARTMENT OF EMBRYOLOGY. 105 



rounding the membranous labyrinth, particular attention being given 

 to the cartilaginous capsule of the ear. This is a favorable place for 

 studying the histological features of the growth of cartilage, for two 

 special reasons: In the first place there are, on account of the intricacy 

 of form of the labyrinth, many kinds of cartilaginous changes found 

 there which are necessary in order to accommodate the growth of the 

 membranous labyrinth; and in the second place the topography is so 

 well marked by known landmarks that all of these changes, as well as the 

 location and direction of growth, can be easily followed. A prelimi- 

 nary report of this study has been published, and therein it is shown 

 that the tissues of the capsule are capable not only of differentiation, 

 but also de-differentiation, throughout a considerable portion of their 

 development. The cartilaginous tissue of the capsule is capable of 

 both progressive and retrogressive changes, and it is this adaptability 

 that makes possible those changes which are necessary in the growth 

 and alteration in form of the labyiinth. 



The work of Dr. Streeter on the reticular tissue surrounding the 

 membranous labyrinth and the histological changes involved in the 

 formation of the scala tympani and scala vestibuli, a prehminary 

 account of which was given in my last report, has now been published 

 in completed form. These spaces have been known since the time of 

 Breschet (1833) as perilymphatic spaces, but inasmuch as they have 

 no apparent relation, either in their manner of development or in their 

 ultimate connection with the lymphatic vascular system, the new 

 term periotic spaces is used by Dr. Streeter for their designation 

 throughout his description of their development. It is found that 

 these spaces have a very definite morphological individuality. They 

 make their appearance at a definite stage in the development of the 

 embryo, they are formed at definite places, they pass through a series 

 of definite histogenetic processes, and they spread in the course of 

 their growth in a definite order and manner; all of which points to the 

 existence of a definite function on their part. 



A critical review of the work which has been done on the lymphatic 

 system during the past fifteen years has been given by Professor F. R. 

 Sabin, in which special attention is devoted to the general subject of 

 tissue spaces and tissue fluids. Professor Sabin calls attention to the 

 fact that these last-named structures are not to be confused with the 

 endotheUal system of lymphatic vessels and urges the restriction of the 

 term lymph and lymphatic to the latter — the true lymphatic system. 

 She has extended her studies on the vascular system to the Uving chick 

 blastoderm, and by comparing the conditions found there with injected 

 specimens of very young chick and pig embryos has been able to make 

 important observations regarding the origin and development of the 

 early blood-vessels. 



The results of this study have been pubUshed in the Contributions 

 to Embryology in Publication No. 226, Carnegie Institution of Wash- 



