202 DEVELOPMENT OF LIMULUS POLYPHEMUS. 



Explanation of Plates III-V. 



Fig. 1. Spermatozoa of Limulus Polyphemus, magnified about 400 diameters. 



Fig. 2. Cell-egg of Limulus attached to the ovarian tube; n, nucleolus, or Purkinjean vesicle; pi, layer of 

 ])roto]ilasm surrounding the nucleus. 2a, epithelial cells lining the ovarian tube, X 210 diameters. 2&, a fold 

 or ruffle of the tube consisting of epithelial cells destined to become eggs, X 210 diameters. 26, 2c, earliest form 

 of the cell-egg, with the nucleus. 2d, the same a httle larger; all X 130 diams. 



Fig. 3. A cell-egg attached to the ovary, X 130 diams. 



Fig. 4. An older cell-egg, with yolk cells developing, X 130. (The nucleus should appear lighter than the 

 rest of the egg). 



Fig. 5. A still older egg with one or two yolk cells nearly as large as the nucleus, w, X 130 diams. 



Fig. 6. A portion of the suiface of the freshly impregnated egg, showing the blastodermic cells, X 30 

 diams. 6a, the same, X 130 diams. 6J, An egg after the primitive cells h.ave disappeared, X 30 diams. 



Fig. 7. The same as 66, a little farther advanced, x — diams. 



Fig. 8. Profile, and 8a vertical view of the blastodermic cells before the amnion is moulted, X 130 diams. 



Fig. 9. Amnion {p) not yet moulted; cA, chorion; y, yolk cells; X 130 diams. 



Fig. 10. The primitive disc (j^m), the curves indicating the protozoonites ; y, yolk; ch, chorion ; X 50 diams. 



Fig. 11. Cells of the amnion after the chorion has split apart, X 400 diams. 11a, profile view of the same 

 less magnified. 



Fig. 1"2. Upper figure pai-tial profile, lower figm-e front view of the embryo as it first appears ; m, mouth. 

 12a, the embryo farther advanced than in fig. 10, and showing at a the amnion beginning to split oif; seen 

 more distinctly at 125, the rest being seen at a. 



Fig. 13. The embryo farther advanced, with the finger-shaped rudimentary limbs. The dotted portion 

 represents the amnion. 



Fig. 14, 14a and 15. The same in a little earlier stage than Fig. 13 ; pni, amnion ; x, j'olk masses detached 

 before the formation of the blastodermic skin. These and 13 represent the naupliiis stage. 



Fig. 16. The beginning of the subzoean stage, signalized by the appearance of the two pairs of abdominal 

 appendages (aJ), and the appearance of the protozoonites on the back of the embryo. 



Fig. 17, front, 17a, profile view of the embryo farther advanced, with the indications of a third pair of 

 abdominal appendages. 



Fig. 18, 18a. The same still farther advanced, showing at z the skin peeUng ofi", being the first subzoeal 

 moult. 



Fig. 19, 19a. The abdomen is now difierentiated from the head, with the segments well marked ; the five 

 lobes of the liver indicating the five posterior ceplialic segments. 



Fig. 20. Posterior view of an older individual, showing the abdominal segments, and the three pairs of 

 gills and the dorsal vessel. 



Fig. 21. Another view, with the abdominal segments left out, but showing the flagrum {/) and the lower 

 edge of the carapace. 



Fig. 22. Rudimentary gills, divided each into two lobes ; the gills are shown in a later stage in fig. 24b. 



Fig. 23. The middle and posterior feet ; d, sixth pair. 



Fig. 24, 24a, 245. Different views of the embryo just before hatching, sho^ving the trilobitic stage of the 

 young. 24c, a middle leg. 



Fig. 25, 25a, 255, 25c. Different views of the freshly hatched young ; c, cardiac lobe, o, opthalmic ridge. 



Fig. 26. Second pair of abilominal appendages of the larva, bearing the gills. 26a, outer or first pair 

 of abdominal appendages; 265, the same, at an earlier stage. 



Fig. 27. Larva after the first moult, having acquired the rudimentary spine, also showing the circulation as 

 seen in the living larva ; the feathered arrows indicate the arteries, and the arrows with a simple shaft the 

 course of the venous currents ; i, intestine. The lobules of the liver are seen in the head and sending two 

 lobes into the abdomen alongside of the mtestine. 



Note. Figs. 16, 19, 19a, 24, 24a, 245, 24c, 25, 25a, 255, 25c, -Ibd, were drawn by Mr. J. H. Emerton. The 

 observations were made with a Tolles' triplet and Zentmayer's Hospital microscope, with his inch and a half 

 and 4-10 objectives. 



