62 THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBAEUS 



influenced by it before they touched it. When a small glass table was used the 

 young also collected under it and reached up as if trying to climb up to it. 

 When dark paste-board was laid on part of the glass, above, twenty-two larvae 

 had collected under that part of the table shaded by the paste-board, in two 

 hours, and none under the clear part. 



It may be imagined from these indications that the larvae in the third stage 

 have a tendency to climb upward due to negative geotactic responses, that they 

 prefer the shade as being photophobic and that they come to rest standing upon 

 a solid object as being thigmotactic. Assuming some such responses together 

 with some chemo tactic phenomena, possibly all the habits of the young in refer- 

 ence to the mother may be explained; possibly not. 



The association of the young and the mother, however brought about, 

 endures in Cambarus affinis during two larval stages and a part of a third. In 

 Astacus leniusculus, however, it is the second and not the third stage which 

 gives up the association with the mother. Whether this is a generic difference 

 cannot be determined without extensive observations, as almost no data are yet 

 at hand. That Cambarus in general have three dependent stages seems prob- 

 able from the following few facts that have been recorded. 



Faxon ('85) saw specimens of C. Clarkii 7 mm. long upon the abdomen of 

 the mother (as previously recorded by Hagen, '70), in which the tail-fan was 

 perfect so that with the ability to lead a free existence there was still the habit of 

 associating with the mother. In C. affinis larvas in the first stage are 4 mm., in 

 the second 5 mm., and in the third 7-8 mm. long, and it seems probable that the 

 above recorded C. Clarkii were also in a third stage. The same author saw 

 upon the mother C. gracilis 9 mm. and C. Bartonii 10 mm. long, with perfect 

 tail fan. These two species may well have three stages of association as in C. 

 affinis. Also he records C. rusticus just hatched and 4 mm. long as being so 

 embryonic that we may assume they would remain with the mother as long as 

 C. affinis does. On the other hand Steele ( :02), who first observed the living 

 larvae of Cambarus associated with the mother, records C. gracilis 7 to 8 mm. 

 long with a bent rostrum as if in the first stage though so large. And in a more 

 detailed study of C. virilis she describes the first stage and then a second stage 

 nine days old with the tail fan complete and other features of the third stage 

 of C. affinis, but as she says the larva six days old could swim it seems prob- 

 able that in both these species as in C. affinis there are three stages in the 

 period of association, the second of which is easily overlooked. 



There is then no obstacle to assuming that we may expect to find in Cam- 

 barus that the larvae remain with the mother through a first, a second and part 

 of a third larval stage and that in Astacus they remain through the first and 

 part of the second only. 



