THE AMERICAN LOBSTER. 241 



Plate 19. 



Fig. 32. First swimming stage of the lobster, usually called tho first larva or the first schizopod 

 stago. Dorsal view. Drawn from life July 3, 1890. The bright vermilion pigment cells 

 or chromatophores of tho skin are here expanded under stimulation. Under some condi- 

 tions they contract, and the animal becomes very pale-blue, in consequence of the blood 

 pigment. The stomach-bag on tho middle lino behind the eyes, the lobes of the yellow 

 ''liver" on either side of this, the heart behind the stomach, and the intestine passing 

 beneath this from the stomach to the hinder end of the body, are clearly discerned through 

 the transparent shell. The yellow cast of color is rather too pronounced, especially in the 

 abdomen. For color of eyes, see p. 169, and fig. 27. Length about 7.8 mm. (-$j inch). 

 Enlarged 22 times. 



Plate 20. 



Fig. 33. Profile view of the first larva of the lobster. Length about 8 mm. July 22, 1891. The trans- 

 parency of these larvae is often very great, and many of the organs, such as the heart, 

 gills, and alimentary tract, are seen with great clearness through the shell. (Compare 

 fig. 32.) The "liver" or gastric gland, usually of a golden-yellow color and resembling a 

 cluster of grapes, is the most voluminous and conspicuous of the internal organs. The 

 shading by stipple in this and the two following plates is purely couventional, no attempt 

 being made to represent the pigmented skin. Enlarged 30 times. 



Plate 21. 



Fig. 34. Second larva; profile view; drawn to the same scale as fig. 33. The second larval stage is 

 preceded by the second molt. Beside the striking increase in size in all the. parts of the 

 body, the most important changes are the growth of the antenna? and the appearance of 

 rudimentary legs or swimmerets on the under side of the abdomen — upon the second 

 to fifth somites, inclusive. Length about 9 mm. (0.35 inch). Enlarged 30 times. 



Plate 22. 



Fig. 35. Third larva; lateral view. Drawn July 15, 1891. The principal changes which are empha- 

 sized at the third molt concern the antennae, the growth of the thoracic appendages, chiefly 

 seen in the large claws, and the acquisition of the last pair of abdominal appendages, 

 which, with the telson, constitute a very important locomotor organ, the propeller or 

 tail fan. Length 11.1 mm. (0.41 inch). Enlarged 22 times. 



Plate 23. 



Fig. 36. Fourth larva; dorsal view. Length 14.6 mm. Drawn and colored from life August 7, 1891. 

 This represents the average normal color of this stage, yet, as will be seen in Chapter 

 XII, this is subject to considerable variation. The brilliant peacock-green or intense 

 yellow-green spots upon the carapace and abdominal segments are characteristic of this 

 period, but it is difficult to represent these pigments in their natural glow and purity. 

 Enlarged 10| times. 



Plate 24. 



Fig. 37. Sixth stage; dorsal view. Outline from a young lobster 15.3 mm. iong, July 14, 1891; color- 

 ing from lobster No. 3, table 34, in sixth stage raised from fourth larva; length 15.5 mm. 

 Enlarged 8W times. 



Plate 25. 



Fig. 38. Young lobster in sixth stage; profile view. Raised from the egg; lobster No. 36, table 34. 

 Length 16 mm. Drawn and colored from life July 30, 1892. The white spots or tendon- 

 marks on the carapace are very characteristic of this period. They are somewhat less 

 prominent in the fifth stage. The fifth stage usually resembles the sixth very closely, 

 particularly in color. Enlarged 11| times. 



F. C. B. 1895-16 



