MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 393 



over till' nervous system (Fig. 221, ad. m.). Closely associatod with it are tiie muscles of tlic 

 maxillie. Tiie large flat tendoi! to wbicli the acUlnctor muscle of the forceps is attached, is well 

 developed at the time of hatching. It is formed liy the infolding of a sheet of ectoilerin cells at tli<i 

 point of articulation of the fingers of the claws, and in a plane at right angles to their plauo of action. 

 The outer ends of the cells of this infolded sheet now o[ti)ose each other and secrete the chitinous 

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



The conuective tissues invest the organs aud 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 fibers appear to be attached to the tergum of the 

 somite (Fig. 196). This may be explained by the intimate fusion of the ectoblast and niesoblast at 

 these points. 



The green gland (PI. Liii, Fig. 198, cuj.) at the base of the second antenna is a well defined 

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

 of the nndgut, aud of a solid, di.sc, shaped body. The walls of the tube arc composed of a single 

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

 solid nodular boily. 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 labrum and into the eyestalks. The solid almond sliai)ed 

 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 which the secretive product ot 

 the gland is due. 



The reproductive organs, or what I regard as such, are ditBcult to find, owing to their very 

 rudimentary condition. They consist of a small cluster of large cells on either side of the mid<lle 

 line between the digestive tract and the anterior end of the heart (Stage x, Fig. 173, K. 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 uuicellidar 

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

 and adult forms. 



II. — THE ORIGIN OF OVARIAN EGGS IN ALPHEUS, HOMARUS, AND PALINURUS. 



(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 (.4. saulci/i) they 

 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 

 biusal 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 abilominal appendages had been laid. The ovarian ova are 

 ripe l)y 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. Tims there is a constant su(;(;ession of young, and females 

 are not commonly foun<l without either attai;hed or large ovaiian eggs. The breeding season of 

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



The stru(!tur(^ of the ovary is (juite simple (Fig. 11). It is essentially a sac lined with ger- 

 minal ei»ithelium. 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 filled with blood. This uuiy ho 

 unnaturally large in the preparation owing to the disturbing edecUs of the reagents emphned, 

 but it is not wiiolly 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 germogen or poly nuclear mass of protoplasm from which the ova are develojjed, 

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



