44 CONKLIN — EMBRYOLOGY OF A BRACHIOPOD. [April 4, 



body cavity, has entirely disappeared. The method of fixation, 

 together with the long residence of the material in alcohol, ren- 

 dered it difficult to stain. The picro-haematoxylin, which I have 

 used with such good results in other cases, was of little value here, 

 and I have found that in the preparation of entire eggs or embryos 

 the most useful stain is borax carmine, while in the preparation of 

 sections iron haematoxylin has given the best results. Both entire 

 preparations and serial sections were mounted in balsam and studied 

 and drawn under an immersion lens (Zeiss. Apochromat. 3 mm., 

 Comp. Occ. 4). 



Perhaps I may be pardoned a word- in defense of the rather large 

 use of surface views and optical sections which I have made in this 

 paper. This has not been due to the fact that I have made few 

 serial sections, for I have made and studied serial sections of many 

 hundreds of embryos, but because with material which is at all 

 favorable the orientation of the embryo and the interrelation of 

 its various parts can be more safely and satisfactorily determined 

 from the study of whole embryos than by means of serial sections ; 

 and this is especially true where it is possible to use an immersion 

 lens in the study of entire preparations. Further, more points of 

 structure can be shown in a single figure of this kind than in dozens 

 of figures of serial sections. Of course, serial sections must always 

 be used in connection with the study of entire preparations, and in 

 the present paper all the details of internal structure which are 

 shown in the surface views and optical sections have been confirmed 

 again and again by serial sections. Any one accustomed to the 

 study of both entire preparations and serial sections knows that few 

 things are more deceptive than the latter when not checked by a 

 study of the former, while the publication of whole series of sec- 

 tions contributes more to the pride of the author and the income 

 of the illustrator than to the edification of the reader. 



II. The Egg and its Cleavage. 



Morse ('71) has described the method of egg laying, and has 

 called attention to the fact that the mature eggs are usually kidney- 

 shaped, though they vary considerably in shape and size. None of 

 the unsegmented eggs which I have examined are kidney-shaped ; 

 they are slightly elliptical, being about 160 /x in the longest diame- 

 ter and 144/^. in the shortest. This elongation of the egg in one 



