NO. 1573. PARASITIC COPEPODS— WILSON. 359 



The lateral plates of the first segment are just starting and correspond 

 closely to the lateral processes of the same segment in the male. The 

 second pair of plates have not started, while the third pair appear as 

 two broad and short lobes on the fourth segment. 



The genital segment is comparatively wider in the female, and the 

 fifth legs are on the ventral surface instead of at the posterior corners. 

 The abdomen is visible for its entire length behind the genital segment 

 and is very similar to that of the male, having only a single joint. The 

 anal lamina? are also similar, and w^hile the spines on them are non- 

 plumose and very short, they are arranged similarly to those in the 

 male. 



The appendages in this young female, liowever, are like those of the 

 adult of the same sex. The terminal joints of the second maxillipeds 

 are in the form of adhesion pads. They have not yet assumed the 

 reniform shape characteristic of the adult, but are otherwise the same. 

 The swimming legs are exactly like those in the adult female, as can be 

 seen from fig. 12, p. 341. 



In the second chalimus, 4 mm. in length, we find the carapace 

 approaching the adult form. The posterior lobes have shortened, and 

 the carapace has widened. The free thorax segments have become 

 more compactly joined, and the dorsal plates are all of good size. 

 Those on the second segment, however, are now circular, and neither 

 they nor the third pair meet at the center, but leave a wide median 

 space between them (fig. 13, p. 342). 



The genital segment has widened and approached more nearly to the 

 size of the carapace. It has also grown backward over the abdomen, 

 so that the posterior margin of the latter is just even with that of the 

 former. Much of the dorsal surface of the abdomen is still visible, 

 however, through the median sinus of the genital segment. 



In the tliird chalimus, 4.5 mm. long, we find practically the same 

 structure as in the adult. The carapace has widened and its posterior 

 lobes have shortened. The eyes have moved nearer the anterior 

 margin, and the frontal plates have become relatively much less 

 prominent. On the thorax segments the dorsal plates have increased 

 in size until they overlap on the mid-line, while the posterior margins 

 of the first and third pairs are handsomely scalloped (fig. 14, p. 343). 



The genital segment has now become a little larger than the cara- 

 pace, while the abdomen has entirely withdrawn beneath it so that 

 only the tips of the anal laminse are visible at the base of the median 

 sinus. 



'S^ariety stimpsoni: Carapace wedge-shaped, one and a half times 

 wider than long, strongly narrowed anteriorly as in dentatus, but 

 with the sides nearly straight instead of strongly convex, and with 

 very short posterior lobes. The under surface of the carapace shows 



