THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBARUS 73 



to the time of egg laying and a retention of embryo-like larv;e upon the mother 

 along with reduction in number of larval stages, that would allow for a long 

 family life and protection of young nearly to the adult state. 



That Cambarus has departed from the ancestral state more than has Asta- 

 cus is shown by the following considerations. In C. affinis the telson is more 

 reduced, that is its shape is less like that of an ancestral swimming organ and 

 its protecting spines are only upon the posterior edge and not along the side as 

 well, and. moi'covcr, there are but 32 as compared with 66 in A. leniusculus or, 

 probably, 5(1 in one Astacus of Europe. Cambarus affinis holds its second an- 

 tennas bent back under the thorax out of the way of jostling neighbors upon 

 the pleopods but in a position of no use as a feeling organ. This antenna is 

 also very short and has but 25 segments as against 50 in Astacus. In Cambarus 

 the appendages of the iirst abdominal segment, which will ultimately be sexual 

 organs in the male, are started in the first stage though lacking till much later 

 in Astacus, as far as known. And the young develop to sexual maturity within 

 four months, thus shortening the period of non-sexual life remarkably. Rathke 

 ('29) found no signs of stylets in male Astacus 1 inch 3-4 lines long while we 

 find them 0.1 mm. long in C. affinis 17 mm. in length. The telson thread of 

 Cambarus seems made less evidently from a recent larval skin and is apparently 

 of earlier origin than in Astacus, as it seems to arise further back in the em- 

 bryonic life ; or we should say the larval history of Astacus is the more primitive 

 in having a more complete representation of a lost larval stage still evident in 

 a complete cast cuticle within the egg. But while there is a cuticle cast off near 

 the time of hatching in both Astacus and the lobster we may assume from com- 

 parison of these larviB that the tirst stage of the lobster is represented within 

 the egg of the crayfish and that therefore the cuticles cast at hatching are not 

 homologous. 



In the second stage of Cambarus there are also signs of further recession 

 fi-oni ancestral states. Thus the rostrum is less developed and not as efficient 

 as a defense as it is in the more active Astacus. The second larva of Cam- 

 barus still lacks most of the plumose set^e that are present in the second As- 

 tacus and is thereby less fit for free life and is also moi-e like an embryo. The 

 second stage of Cambarus lives upon the mother while in Astacus it becomes 

 free : in Cambarus it is fast by its chehe and when it moults a delay in casting 

 off the cuticular lining of the intestine makes an anal thread that mechanically 

 continues the attachment of the young to the mother beyond what is found in 

 Astacus. The telson of Cambarus affinis, even in the second stage, has only spines 

 in place of the locomotor plumes of Astacus and is thus evidently unfit for free 

 life. Cambarus also has not yet developed sense setae upon the second segment 

 of the exopodite of the second antenna and is thus not as advanced as Astacus 

 is; and the ear pit is less jierfected in not having the seta^ along its edge. The 



