195] REGENERATION OF CRAYFISH APPENDAGES 7 



Decapods belonging to several different genera, to different 

 families even, were used in the third series of experiments ('99), 

 but in all cases the results were similar to those obtained in the 

 previous experiments. But in this latter investigation, the ob- 

 servations extended over a much greater period of time than in 

 the previous ones, and consequently a number of details were 

 brought out here that had not been observed before ; for exam- 

 ple, Herbst found that the regenerated structure increased in 

 length and in number of segments as the length of time and num- 

 ber of moults increased; and also that the number of rows of 

 sensory hairs, born by the flagella, became more numerous, one 

 case being recorded in which the number of rows of hairs in- 

 creased between two successive moults from 21 to 33. Several 

 instances are mentioned in which the flagellum was 2.5 to 3 cm. 

 in length and consisted of no to 150 segments. Herbst also 

 determined the regenerative capacity of the heteromorphic struc- 

 ture, and found that after removal of either the whole or a part 

 of it a similar structure was again regenerated. 



At the close of the third series of experiments, there is given 

 a resume of the chief facts observed up to this time. The main 

 points brought out are as follows : "Experiments upon Palaemon 

 squilla, P. rectirostris and P. serratus, Palaemonetes varians, 

 'Sicyonia sciilpta, Astacus fluviatilis, Palinurus vulgaris, Scylla- 

 rus arctiis, and Eupagurus psideauxii show that after total ex- 

 cision of the eye, an eye is never regenerated, but instead, when- 

 ever regeneration takes place, there appears a heteromorphic 

 structure which always resembles more or less an antenna. 

 Some portion of this regenerated structure is always provided 

 with long sensory hairs which, in some instances, are developed 

 on both the basal and the distal regions." A point worthy of at- 

 tention in the consideration of these experiments is the diversity 

 of forms that were used as material for experiment. Individu- 

 als belonging to three widely distinct families were used and still 

 the results were in the main identical. 



