90 E. A. ANDREWS. 



No doubt the general elevation later becomes the triangle and 

 is comparable to the knob found in Cambarus, but the meaning 

 of the lateral pit is problematical. Possibly it is the forerunner 

 of the cavity at the end of the triangle which gives it the extin- 

 guisher-like form, and which being still more prominent in the 

 English Astaais may be an old trait that would more likely find 

 expression in the older genus, Astacus, than in the newer one 

 Cambarus . 



By way of summary we will state that the first stylet of these 

 crayfishes, Cambarus and Astacus, has the anatomy of a pleopod 

 that has lost both its biramous form and its intrinsic muscles and 

 has become a nearly closed tube. In its physiology it is essen- 

 tially a tube to transmit the sperm from the male to the female. 



The ontogeny throws little light upon the phylogeny of the 

 organ since at its first appearance in the larva it is already a 

 simple papilla, which in Astacus becomes a flat plate that then 

 rolls in to form a tube while in Cambarus it forms a tube by 

 thickening of the edges. 



The apparent simplicity of the first stylet in Cambarus misled 

 Hagen (3, p. 17) to regard it as having lost its channel save for 

 the external groove, while in reahty there is a functional inner 

 tubule. 



The anatomy of the first stylet of Cambarus gives a firm basis 

 for the interpretation of the various terminations of this organ as 

 exhibited in different species and made use of for detecting genetic 

 relationship as well as specific characters. It will be necessary 

 to restudy the stylets of all Cambari to determine in how far the 

 accepted morphological division into " inner " and " outer " parts 

 is a sound basis for comparisons. In each species the canula, or 

 real termination of the organ, must be distinguished, and the 

 various secondary outgrowths classified as to their origin from 

 the two sides of the groove that ends at the tip of the canula. 

 With this knowledge a more scientific understanding of the genus 

 may be possible. The " outer" part seems to be the canula or 

 real end of the organ and the " inner" part only a lateral out- 

 growth from one side of the canula. The two are not of equal 

 import.'^ 



1 In practice stains that enter the canula tubule will aid in recognition of the 

 canula without the need of sections. 



I 



