No. 2.] EMBRYOLOGY OF THE AMERICAN LOBSTER. 245 



lifted from the surface by the lateral tucking under of the ecto- 

 derm (**). The position of the mesoderm cells within the 

 cavity of the appendage is interesting. In several places the 

 ectoderm may be seen to present more than a single layer of 

 nuclei. Chromatin elements are not specially abundant. 



The section (Fig. 6) through 6 of Fig. 3, shows the second 

 antennae actually cut off from the underlying mesoderm, though 

 not separate from the ectoderm. 



In Fig. 7, a section through the proctodasum, is shown the 

 very slight elevation of the thoracico-abdominal plate. The 

 ectodermal cells are clearly invaginated at A. The mesodermal 

 and entodermal elements are seen, as in the previous stage. 



Stage L. 



The figure of this stage on PI. XIV shows the increased con- 

 traction of the embryonic tract, and the forward migration of 

 the second antennae. 



Stage M. 



Perhaps the most interesting feature of this stage (PI. XIV, 

 Fig. M) lies in the fact that the embryonic area, which early 

 occupied nearly one-half the surface of the egg, has now con- 

 tracted until it has reached its greatest point of concentration. 

 This embryonic contraction has been observed to characterize 

 the early developmental stages of several Crustacea. Surface 

 views of fresh and alcoholic eggs show the embryo to be pro- 

 vided with well-rounded appendages (PI. XIV, Fig. 1). 



The antennae have, in relation to the mouth, passed still far- 

 ther forward. The second antennae are clearly biramous, and 

 have also advanced considerably towards the head end. The 

 " third " pair of appendages is still rudimentary. The upper 

 lip has covered the stomodaeum, while the proctodaeum is now 

 quite evident, between the two halves of the telson flap, or ter- 

 minal portion of the thoracico-abdominal fold. The region of 

 the eyes has been somewhat changed. Anteriorly and laterally 

 are to be seen two somewhat specialized tracts, one on either 

 side (Fig. 1, Ce.), from each of which there passes towards 

 the median line a very slightly elevated ridge, terminating in a 

 pair of anteriorly placed elevations (G. 2 ). I am inclined to 



