Ai-tT. XII. — Note from the Biological Laboratoiy of the 

 Melbourne University : — On a Crayfish zvith abnor- 

 mally developed Appendages. 



By Arthuii Dendy, D.Sc. 



[Read 14.th July, 1893.] 



In the five posterior thoracic limbs, or ambulatory appendages, 

 of the common fresh-water Crayfish, the exopodite has, as a rule, 

 completely disappeared, and the limb is formed of protopodite 

 together with very strongly developed endopodite. 



Professor Huxley, in his well-known works on the Crayfish,* 

 referring more particularly to the European Astacus, observes, " I 

 have not been able to discover, at any period of development, an 

 outer division or exopodite in any of the five posterior thoracic 

 limbs. And this is a very remarkable circumstance, inasmuch as 

 such an exopodite exists in the closely allied lobster in the larval 

 state ; and, in many of the shrimp and prawn-like allies of the 

 Crayfish, a complete or rudimentary exopodite is found in those 

 limbs, even in the adult condition." 



The common Australian Crayfish ( Astacopsis bicarinatus) agrees 

 very closely with the European form as regards the thoracic 

 appendages. A few weeks ago, however, when we were dissecting 

 this Crayfish, obtained in quantities from the University pond, one 

 of the students called my attention to a peculiarity in the speci- 

 men with which he had been provided. 



On examining this specimen I found that small exopodites were 

 present on three of the ambulatory appendages, viz.., on the great 

 chela and the succeeding appendage on the right side, and on the 

 great chela alone on the left side. In size, shape, and position 

 these abnormally developed exopodites closely resemble the 

 normal exopodites of the third maxillipede. The specimen is a 

 female, of moderate size. 



The presence of these abnormal exopodites, which, so far as 1 

 am aware, have not hitherto been observed in any true Crayfish, 



*■ International Scientific Series. 



