Segmentation of the Egg of Bdellostoma 49 



of arms and armor in the Metropolitan Museum of Art. However, the American Mu- 

 seum was not ready to lose him entirely and he was made honorary curator of fishes — a 

 post which he held until his death. Under the circumstances set forth he never found 

 time to take up the projected further work on the segmentation of the egg of Bdellostoma. 



The publication of Doctor Dean's exquisite drawings of the segmentation of the 

 egg of Bdellostoma stouti has been undertaken by us, one his former pupil and both his 

 longtime friends, that they may not be lost to science and that their publication may be a 

 memorial to their maker. These figures, in storage for 30 years, had undergone some 

 deterioration, in particular the board on which they were drawn had become stained and 

 yellow with age. Their preparation for the lithographer was entrusted to Mr. W. H. 

 Southwick, who has skilfully cut out the figures and has mounted them without any re- 

 touching in such a way as to bring out their artistic as well as their scientific value. 



Since we could find no Bdellostoyna eggs in cleavage stages that had not been sec 

 tioned, we at first thought that we could not do more than write a running text consisting 

 of expanded captions for the various figures. But as we have studied the drawings and the 

 few notes left by Dean, we have been able in a certain degree to describe the segmenta- 

 tion as if we had before us it not the Living eggs at least preserved material. The results of 

 our studies will now be set forth. 



THE EGG 



The structure of the unsegmented egg and of its membranes has been adequately 

 described by Dean in his memoir cited in the introduction, and our information on this 

 subject has been gained from his paper as well as from an examination of entire eggs and a 

 few serial sections of eggs found in Dean's collection. In his 1899 memoir he says: — 



"The egg of Bdellostoma ... is bean- or sausage-shaped, measuring about 22 mm. in length 

 and about 8 mm. in width. Its color is hidian-yellow. It is encased in a horn-like shell, which 

 is thinnest at the midcircumference of the egg and thickest at the ■ends, a membrane as transparent 

 as common tracing paper. One end of the egg is slightly larger than the other, is pierced by a single 

 polar micropyle and is circumscribed by an opercular groove, which enables the terminal portion 

 of the shell to be thrown off like a cap at the time of hatching. . . . The eggs taken on a spawning 

 ground are in nearly every instance fastened together in clusters or bunches [by the anchor fila- 

 ments shown in our text-figures 1, 2, and 3 herein]. 



Specifically Dean notes a considerable variation in the siz,e of the egg: "The egg- 

 length varies . . . between 14.3 and 29 mm. The average of 70 eggs was 22.8, of which 

 number 50 measured between 21 and 24 mm." 



The egg of Bdellostoma possesses a definite polarity, which has already been indicated 

 by the shape of the egg as a whole, by the presence of the opercular cap, and by the micro- 

 pyle in the center of the cluster of anchor filaments at the animal pole. The outer egg 

 membrane or shell, it is interesting to note, is produced by the ovarian follicle and not by 

 an oviduct as in the case of many other vertebrates. The recess just above the micropyle, 



