142 Journal of Comparative Neurology and Psychology. 



tions of the Lvnulus embr)-os was shortly before the lime of 

 hatching.' At this stage the embryo has a distinctly limuloid 

 appearance in nearly all respects. Ail the appendages are 

 formed, and are movable, with the exception of the long telson 

 characteristic of the animal in later stages. The legs are formed 

 on the same plan as those of the adult female, the secondary 

 sexual modifications of the chelae of the first pair of walking 

 legs in the male, not yet appearing. In this and the succeed- 

 ing stages the embryos have a general, superficial resemblance 

 to a trilobite wiiich has led to the designation of these as the 

 "trilobite stages" in the development The embryo lies in the 

 "vicarious chorion" (cf. Packard '72, and Kingsley, '85, p. 

 525) surrounded by fluid. The "vicarious chorion" is consid- 

 erably greater in diameter than any dimension of the embryo, 

 so that there is considerable free space on all sides of the latter. 

 The embryo at this stage is about 4 mm. in length. The fol- 

 lowing account of the behavior within the "vicarious chorion" 

 applies to embryos at any time within a week before hatching. 

 Closer time relations than this, as will appear from the account, 

 cannot be fixed in the development of the reactions of this or- 

 ganism. 



Nonnal Position of the Embryo. — The embryo lies at the 

 bottom of the hollow spliere formed by the "vicarious chorion," 

 with its neural side uppermost. This position is simply the re- 

 sult of the action of gravitation, the embryo sinking to the 

 bottom of the sphere because of the fact that its specific gravity 

 is greater than that of the surrounding fluid. The reason for 

 its lying with the neural surface uppermost is to be found in the 

 fact (to be brought out in detail in another connection) that it 

 is unable, under the circumstances in which it finds itself, to 

 get into and retain any other position in which it is in stable 

 equilibrium. 



Movements ivithin the " Vicarious Chorion." — In the descrip- 



' I shall speak of the developing organisms throughout as "embryos." The 

 rupturing of the "vicarious chorion" and beginning of free larval life, will be 

 termed the "hatching." These expressions are used merely for verbal con- 

 venience. 



