ENTOMOSTRACA OF MINNESOTA. 327 



la the adult Cypris Herricki the caudal margin of the shell is entire. 

 But in stage A, the caudal margin of the shell is bordered with minute 

 teeth (Fig. 34). In this stage the teeth are quite small and might 

 easily be overlooked; but in stage B (Fig. 35), these teeth have become 

 very conspicuous. Indeed, they are the characteristic feature of the 

 shell. These teeth are present throughout stages A to D, but in stage 

 D they have beguu to disappear. In the adult stage there is no trace 

 of these teeth. 



A careful study of the adult shows that the shell is covered with 

 hairs. These hairs are very conspicuous in stage A. The shell of the 

 adult is marked with very conspicuous dark bands. 



An effort has been made to discover at what period these bands 

 appear, and to see if they conform to the rules laid down by Professor 

 Eimer. The characteristic bands on the shell may be present in any 

 stage from A to the adult; and when they are present they do not differ 

 essentially from the markings on the adult. The chief points of dif- 

 ference being variations in the width of the bands. In all examples 

 of stages Cand D examined, these characteristic markings were found; 

 but in stages A and B, they were occasionally absent. An examination 

 of Fig. 35 will show that some of these bands are longitudinal while 

 others are oblique. 



Professor Eimer has attempted to establish the following rule for 

 the formation of oblique markings on animals.* Oblique markings 

 first appear as longitudinal lines. These lines become resolved into 

 dots, these dots, in turn, rearrange themselves in oblique lines. If 

 these laws were aj^plicable to the markings on Cypris Herricki, in 

 stages A and B, where we have some specimens with bands and others 

 without them, we ought to find some transition stages — some stages in 

 which the oblique markings were represented either by parallel lines, 

 or by series of dots. But such is not the case. The shell is either un- 

 marked by bands, or both oblique and longitudinal bands are present. 



As stated above, in stage A the appendages have practically as- 

 sumed their permanent form. The post-abdomen is a notable excep- 

 tion. This appendage is quite rudimentary; not only has it not yet 

 acquired the typical number of seta^-, but the longest terminal seta is as 

 long as, or longer than, the remainder of the post-abdomen. This 

 great relative length of the terminal seta is due, not to an over-devel- 

 opment of the seta, but to an underdevelopment of the body of the 

 post-abdomen. That the post-abdomen appears to be the last append- 

 age to development is rendered more striking by the dis<:',overy of C. 

 Clans that the post abdomen appears before the formation of the sec- 



*G. H. Th. Eiinir. Organic Evolution as the Result of the laheritanse of Acquired Characteis 

 According to the Laws of Organic Growth. Translated by J. T. Cunningham, 1890. f.li. 



