No. I.] THE EMBRYOLOGY OF LIMULUS. 5 1 



July 31, there had appeared inside this rim the remaining pairs 

 of cephalothoracic appendages." 



Although I have looked carefully for the appearances thus 

 described, I cannot confirm the description. Still, there are so 

 many anomalies in the history of many eggs that it is possible 

 that the conditions witnessed by Professor Osborn may some- 

 times occur. For instance, in some eggs, after the somites are 

 partially outlined, a deep longitudinal groove appears, transverse 

 to the somites and extending the whole length of the embryonic 

 area. The lips of this groove sometimes even touch each other, 

 and in the tube thus formed the limbs bud out. Again, in other 

 eggs a deep invagination may take place in the abdominal region, 

 carrying in with it the abdominal feet. Such eggs appear later 

 to regatn the normal appearance and to develop in the regular 



manner. ^ u 4. 



Concerning the later features of external development but 

 little needs to be said. The figures given by Packard Dohrn, 

 and myself are sufficient to indicate most of the features of the 

 growth of body shape and the positions and changes of forms of 

 the various appendages. 



Stage E (= Kingsley, 85', Fig. 5 ; Packard, '72, Fig. 12). -In 

 this stage the edge of the carapax has been differentiated, form- 

 in- a clear-cut line marking off the ventral from the dorsal sur- 

 face The six pairs of cephalothoracic legs retain. a post-oral 

 position, while the first pair (operculum) of abdominal appen- 

 dages is outUned.^ 



5^^^^ i^ (Packard, Fig. 12; Self, '85, Fig. 6; present article, 

 pio- 28) —In this stage the embryo is much as before, except 

 that the second (first gill) appendage of the abdomen has made 

 its appearance, while the series of sense (?) organs briefly men- 

 tioned by Patten ('89, p. 602) are prominent, especially in mounts 

 peeled from the egg and in osmic acid preparations. These 

 sense organs, to which I shall return later, are six in number on 

 either side of the body. I earlier ('90) described their fates, which 

 are as follows: The first pair give rise to the median ocelli of 

 the adult ; the second move to a position in front of the mouth, 

 where near the median line they form a peculiar sense organ 

 as yet undescribed ; the third and sixth disappear at a very 



1 This is not well shown in Packard's figures. 



