AMERICAN PARASITIC ARGULIDJE— WILSON. 



673 



They also change their position slowly, and finall}^ come to occup}^ 

 the whole central space beneath the stomach and intestine. 



The heart can now be delinitely located in the posterior thoracic 

 segment as a triangular pouch with three valvular openings, one 

 median and two lateral, backward into the abdomen, and a large aorta 

 extending forward along the median line to the region of the ])rain. 

 The two lateral posterior openings discharge blood into the side sinuses 

 of the abdomen during diastole, while the flow of blood backward 

 through the central opening is regulated by the transverse!}' pulsating 

 flap or curtain already described. The aorta pulsates with the heart, 

 but the evidence seems to be in favor of regarding it as an aorta (Claus) 

 rather than as the vestibule of the heart (Ley dig), since it corresponds 

 exactl}^ in position and form with the aorta in many copepods, and is 

 also destitute of any side openings. 



Fig. U.— Anterior maxilliped of foliaceus larv. 

 from a claw to a sucking disk (from claus). c 



ITS MATERIAL USED TO MAKE THE NEW DISK d.; tit 



. AFTER SEVERAL MOULTS, SHOWING TRANSITION 

 ., OLD CLAW BEING GRADUALLY ABSORBED AND 



, MUSCLES. 



The other changes at this molt are very slight; the first maxillipeds 

 become somewhat thickened through the middle joints, making them 

 spindle-shaped, and along the central axis in between the muscles may 

 be seen a column of large elliptical cells wdth well-marked nuclei, from 

 which are soon to be developed the sucking disks. These cells are 

 present and distinctly visible in the megalops larva before the first 

 molt. 



A second shedding of the skin takes place three or four days after 

 the first, and produces no perceptible changes except in size and in 

 further development of the sucking disks on the first maxillipeds. 



The second molt occurs about the tenth day, the third on the thir- 

 teenth or fourteenth day, the fourth on the sixteenth day, and the 

 fifth on the twentieth day. During this time the larva gradually 

 increases m size, and the details of structure both external and internal 

 conform more and more to the adult form. This is especially notice- 

 Proc. N. M. vol. XXV— 02 43 



