﻿8 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 102 



nal boundary, always well marked and often formed as a ridge in the 

 integument (fig. 20), which delimits the leg-bearing area. This area 

 may be divided into "segments" coinciding with the legs but totally 

 independent of the boundaries between the body-rings. Zaddach 

 (1841) has ah-eady described the ventral "segmentation" and the 

 corresponding division of the longitudinal muscles in this area in 

 Apus cancriformis . 



3. In two cases of abnormal growth of the body-rings that I have 

 found, the series of legs is not affected by the abnormal turns, or spiral 

 growth, of the related body-rings (fig. 17). 



The first two points hold good for each of the species of Notostraca 

 that I have examined, though some of the details may be difficult to 

 observe m specimens which have just molted or are badly preserved. 



It is a well-laiown fact that the rate of production of new 

 body -rings (in early postembryonic stages) is quite different from 

 that of the legs, with their muscles and nerve-cord ganglions. From 

 the caudal end of the series of legs there are produced, at an 

 almost frantic rate and in considerable number, the elements of the 

 leg-bearing area, but the body-rings, budding from the anterior margin 

 of the telson, increase in number relatively slowly. The body-rings 

 do not vary much in size, but the elements of the leg-bearing area 

 grow smaller and smaller caudally, as if the animal meets the frantic 

 activity of this part with something lil^e starvation of its individual 

 elements. We might assume a kind of organizer at the end of the 

 series of legs (for what else could we assume?) that is, in some way 

 or other, less favored than the ordmary organizers at the anterior 

 boundary of the telson. 



I have noticed in many specimens that this disproportionate 

 development has continued during the further growth of the animal. 

 Thus, we often notice that in a larger animal the series of legs covers 

 a smaller number of body-rings than is the case in a smaller animal 

 in the same lot (see table 2), indicating that the size of the body-rings, 

 but not necessarily their number, increases faster than does the series 

 of legs. Other facts also point to this conclusion: an oblique striation 

 occurrmg at the area where the body-rings and the series of legs meet, 

 explained as the mark of a tension between the two parts as they grow 

 at dissunilar rates; and the moving forward of the fiftieth pair of legs, 

 as observed in table 2 (we note that this moving forward does not 

 exactly follow the changes in size, but individual variation in these 

 complicated processes is to be expected). 



NUMBER OF BODY-RINGS 



It seems to be the rule that neither the total number of rings nor 

 the number of abdominal leg-bearing rings is given in descriptions 



