390 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.xxxiii. 



exactly, leaving no space around its margin. That this is really the 

 rudiment of a sixth thoracic lobe and not a part of the abdomen, as it 

 has been hitherto regarded, is proven in several ways. First, by anal- 

 ogy, it corresponds exactly to the similar lobe found in Dinematura (see 

 p. 374) and Echthrogaleus (see p. 362). Again, it is not connected with 

 the abdomen, but is raised some distance above the dorsal surface of 

 the latter (fig. 17). Furthermore, it is not a fusion of two plates, but 

 is unpaired and median from the very beginning (see fig. 182) . In the 

 matured female it is always above the egg strings, while the abdomen 

 is below them. If it is to be regarded as a dorsal abdominal plate, 

 therefore, we have the anomaly of the egg strings passing through the 

 abdomen, or at least beneath its dorsal plate. Some writers have 

 claimed this very thing, but it is entirely without precedent, and 

 would constitute an anatomical freak of the most capricious sort. 



On the other hand, if this be the rudimentary sixth segment, every- 

 thing is exactly as in the other genera; the egg strings come out from 

 the ventral surface of the genital segment, beneath the sixth segment 

 and above the abdomen exactly as they do in Dinematura and 

 Echthrogaleus. 



Finally, we have the testimony of the male, in every species of 

 which, so far as known, a sixth pair of legs is prominent on the genital 

 segment as well as a fifth pair. 



Such cumulative evidence is convincing and fairly proves that 

 the dorsal plate can not belong to the abdomen, but must represent 

 the sixth segment. 



The ventral plate, on the other hand, does remain in contact with 

 the ventral surface of the abdomen to the very tip of the latter. As 

 a consequence the terminal half of the abdomen is drawn down to 

 the plate tightly and lies along its dorsal surface. As the two lobes 

 at the tip of the abdomen on either side of the anus fuse with the 

 ventral plate, the tips of the lobes themselves also fuse with each 

 other and the anus ceases to be any longer terminal, but opens up. 

 dorsally from the surface of the ventral plate. When the genital seg- 

 ment is thickened by the maturing of the eggs and the coiling of the 

 distended oviduct, the dorsal plate of the sixth segment and the ven- 

 tral plate of the abdomen are separated some distance from each 

 other, while the body of the abdomen lies between them (fig. 17). 



Wlien the eggs finally emerge into the egg strings, the latter are 

 pushed through the spaces between the posterior lobes of the genital 

 segment and the body of the abdomen, above the ventral plate of 

 the latter. They do not, therefore, pass through the abdomen at all, 

 but are entirely outside of it. In this way, although the openings 

 of the oviduct are some distance apart, the egg strings are brought 

 together on the mid line and carried backward side by side so close 

 together as to be often in actual contact. 



