410 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



Wandering cells still occur in all parts of the yolk, though in far less abundance than in 

 earlier stages. We find numbers of them moving toward the periphery, or next the body wall to 

 take part in forming the endodertu. The epihlast is conspicuous in Fig. 108 just in front of the 

 optic lobes. This corresponds in position with the dorsal plate (Fig. 153 <lp.), and is probably a 

 remnant of it. The small clusters of cells beneath it and the degenerative products which occur 

 near them, probably also represent the remains of the great swarm of degenerating ehroinatiu 

 particles which was formerly present in this region. A blood space (Fig. 108,) now extends over 

 the dorsal side of the egg between the epiblast and the yolk, from the heart to the optic lobes and 

 region of the head. 



Anteriorly we can distinguish in transverse section three vessels a median impaired one, 

 which answers to the ophthalmic artery, and a pair of lateral vessels, the an ten nary arteries. 

 The vascular walls are extremely delicate and contain flattened cells, the nuclei of which in longi- 

 tudinal sections appear almost linear. Seen from the surface of the egg the blood vessels have 

 the appearance of two bands of tissue, passing backward from near the point of union of the 

 optic lobes. Between and at either side of the optic lobes, and beneath and to each side of the 

 brain, we find blood spaces packed with corpuscles (Figs. 100-109, It. 8.) It is not possible, in 

 most cases, to distinguish at this phase true sinuses (veins) from arteries. The structure of the 

 heart is shown in Figs. 164 and 108 (H.), and is essentially the same as in Stage IX. 



In Fig. 173 there is a small solid cluster of peculiar cells (R. 0.) on either side of the alimen- 

 tary tract, between it and the heart. This I regard as the rudiment of the reproductive organ. 

 The cells are clearly differentiated from the surrounding cells. The nuclei are very large, spher- 

 ical, and stain lightly and diffusely. They are enveloped in a capsule of mesoderm cells, like those 

 forming the walls of the heart, and they originate from similar elements. In Stage ix (Fig. 157) 

 these cell masses were first recognized. They are then distinct from the surrounding elements, 

 and the nucleus contains a very delicate reticulum. Each celt cluster is so small that unless the 

 sections are uniform and complete it is very easily overlooked. The muscles have developed in 

 various parts of the body (Figs: 108, 171, 172, mu., mu. /., mu. e., tj. in. .), but most striking at 

 this stage are the great flexor and extensor muscles of the abdomen. 



The green gland (Fig. 170, A. U.) is another organ which we now meet with for the first time. 

 It is an irregular tube, closed at both ends, and lies at the base of the second antenna, extending 

 up a short 'way between the body wall and brain. In the previous stage all the tissue at the root 

 of this appendage is very loose and reticular, and no lumen can be seen. I have been unable to 

 detect any opening of the gland to the exterior, nor should we expect to find any, since, as we 

 have already seen in Section i, there is none in the larva. It must be regarded as a mesodermic 

 structure. 



STAGE XI. EMBRYO OF ALPHEUS HETEROCHELIS NEARLY READY TO HATCH. 



The later stages (Stages vi-x) have had reference to a single species of Alpheus, namely, 

 Alphi-us xtuilfi/i, the larva of which is described in the first section. The embryo of Aliiltcnx 

 In ti'fiichdin at about the time of hatching is considerably less advanced than the embryo of the 

 first species at a similar period, and will serve in many respects as a convenient connecting link 

 between the larva described in Section I and the, last stage. The embryo of Alpheus heterochelix is 

 represented by a longitudinal vertical section and by a series of transverse ones (I'ls. L, LI). The 

 longitudinal sections of Stage x, of this stage, and of the larva (Figs. 10S, 180, 190), form a very 

 interesting series for comparative study. 



The eye and the ganglia of the eye stalk (Figs. 177-179, 187) have become highly specialized, 

 and closely resemble the adult organs. The brain is larger, but shows no new structures which 

 have not already been noticed. The entire nervous system is more compact, and is completely 

 separated from the skin. The foregut is larger than in the previous stage, and the walls 

 of the masticatory stomach have become very much thickened. It is screened from the yolk 

 by a membrane composed of large cells, which extend backward over the nerve cord. A double 

 band of muscles (Figs. 168, 180, g. m. a.) passes upward from the anterior wall of the masticatory 

 stomach and from the brain, to the body wall. These will be referred to the anterior gastric 

 muscles. 



