MEMOIRS OF TtlE NATIONAL AC A UK. MY OF SCIKNCES. 393 



over the nervous system (Fig. 2lil, ad. in.]. Closely associated with it are the inn.M-lex of the 

 maxilla^. Tlie, large flat tendon to which the adductor muscle of the forceps is attached, is well 

 developed at the time of hatching. It is Conned by the infolding of a sheet of ectoderm cells a I I lie 

 point of articulation of the tinkers ol'the claws, and in a. plane at right angles to their plane of act ion. 

 The outer ends of the. cells of this infolded sheet now oppose each other and secrete the chitinons 

 tendon, while to their morphologically iinirr ends the muscle libers are attached. 



The connective tissues invest the organs and seem to bind them together and to suspend them 

 to the outer ectodermal wall of the body, but in some cases the ectoderm of the surface is apparently 

 replaced by mesoderm cells, and often muscle libers appear to be attached to the tergum of the 

 somite (Fig. 190). This may be explained by the intimate fusion of the ectoblast and mesoblast at 

 these points. 



'The green gland (PI. LIII, Fig. 198, ay.) at the base of the second antenna is a well delined 

 structure. It consists of a blind tube, which passes up close to the brain as far as the anterior sacs 

 of the midgut, and of a solid, disc, shaped body. The walls of the tube are composed of a single 

 layer of large cubical cells. These thin out at the lower end, and to the outer wail is applied the 

 solid nodular body. Neither at this stage nor at any previous one have I been able to detect an 

 opening to the exterior. 



In the adult the tubular portion of the gland grows to very great length, coiling itself in all the 

 available space in the anterior region of the body in front of the mandibles. It surrounds the brain 

 and oesophagus and passes down to the labriun and into the eyestalks. The solid almond shaped 

 body (probably the end-sac) becomes a spongy mass of tissue. Its function is plainly different 

 from that of the epithelium which forms the wall of the tube and to whicli the secretive product ot 

 the gland is due. 



The reproductive organs, or what I regard as such, are difficult to tind, owing to their very 

 rudimentary condition. They consist of a small cluster of large cells on either side of the middle 

 line between the digestive tract and the anterior end of the heart (Stage x, Fig. 173, 1\. O.). 



With this sketch of the structure of the larva we are ready to trace the history of develop- 

 ment from the earliest stages and to ascertain the manifold changes through which the unicellular 

 egg with its great store of yolk passes, before it attains to the wonderful complexity of the larval 

 and adult forms. 



(a) Alpheus. The ovaries of Alpheus are paired cylindrical bodies which extend 'between the 

 alimentary tract and dorsal blood vessels, from just behind the eyes to the end of the third or 

 fourth abdominal somite. Owing to the transparency of the skin in this species (A. xanlci/i) the.x 

 are extremely conspicuous, giving to the female an intense green or yellow hue, according to the 

 color of the egg (PI. iv). The oviducts open in the usual way by means of a slit-like'valve on the 

 basal joint of the third pereiopods. 



In PI. xxvi, Fig. 11, the condition of the adult ovary is shown, as it appears two or three days 

 after the eggs then carried on the abdominal appendages had been laid. The ovarian ova are 

 ripe by the time the young are ready to leave the shell, and the new ova are laid in a few hours 

 after the hatching of the larval brood. Thus there is a constant succession of young, and females 

 are not commonly found without either attached or large ovarian eggs. The. breeding season of 

 this species extends, as we have seen, throughout the entire year. 



The structure of the ovary is quite simple (Fig. 11). It is essentially a sac lined with ger- 

 minal epithelium. The external layer of the sac (O. W.) is muscular and contains numerous nuclei. 

 Between the epithelium and fibrous coat there is a wide space tilled with blood. This may be 

 unnaturally large in the preparation owing to the disturbing effects of the reagents employed, 

 but it is not wholly abnormal. The germinal epithelium consists, for the most part, of a single 

 layer of large cubical cells. The nuclei are large and granular, and the cell outlines are often 

 distinct. The function of these epithelial cells is twofold: (1) They give rise to ova; (2)"They 

 form the epithelium of the egg follicle. 



There is no germogeu or poly nuclear mass of protoplasm from whic.li the ova arc developed, 

 but the eggs appear to originate directly from epithelial cells. The new eggs begin to develop, 



