189S.] APPEJTDAGES IN THE ARTHROPODA. 935 



limb right down to its extremity were present and identifiable) 

 are features generally found in Tracheates. It would appear 

 that the formation of the new appendage is a very rapid 

 process, and the facts are favourable to the view that ecdysis 

 really involves more or less reconstruction of the soft parts as well 

 as of the cuticle. This, however, can hardly be the case in Crusta- 

 ceans, in which the new growth is distinctly a reproduction of the 

 limb W'hile still covered by a cuticle. 



(b) Relative Dimensions of the Tarsal Joints. 



The reproduced femur and tibia resemble those of the normal 

 congenital limb, though they are always smaller than the latter at 

 their first appearance. In one or two cases I have f oimd the tibia 

 of arcuate form, but this condition was probably due to incomplete 

 straightening from the coiled-up condition before ecdysis. The 

 reproduced tarsus is, however, always four-jointed, though in 

 certain very exceptional cases to be shortly described this condition 

 was not quite fully expressed. It is never five-jointed as in the 

 normal. 



The general appearance of a normal and of a reproduced tarsus 

 from the same pair of legs of an adult Periplaneta ameiicana is 

 shown in Plate LVIII. figs. 2 & 3. The following table gives 

 examples of the relative lengths of the tarsal joints of both normal 

 and reproduced forms. The measurements were made along the 

 dorsal side and with the tarsi as much extended as possible. It is 

 obvious that this method imposes undue prominence on the lengths 

 of the proximal and terminal joints, on account of the telescoping 

 of the intermediate joints into the above and into each other at 

 their articulations, but the results are sufficient for comparison as 

 the treatment was uniform. The tarsi of small nymphs were 

 measured with a micrometer eyepiece, and those of large nymphs 

 with a sliding screw micrometer kindlv lent to me by Professor 

 W. P. E. Weldon. 



In these tables and later on the several joints of a tarsus or 

 other appendage are for brevity referred to as j^, j^, &c. in the 

 case of normal congenital structures, and as J^, J.^, &c. in the case 

 of reproduced structures, the numeration beginning with the 

 proximal joint. 



In the following tables the total length of the tarsus was 

 reduced to 100 in each case, and the lengths of the several joints 

 are expressed as percentages. 



Table B. — Periplaneta americdna. 



5-jointed tarsi. Means of measurements of 115 tarsi from the third pair 



of legs. 



Ji' J2' 3v 3v Js' 



53-2 15-6 9-5 49 16-8 



A-jointed tarsi. Means of measurements of 115 tarsi from the third pair 

 of legs. 



Jj. Jj. J3. J4. 



57-4 18-3 6-4 17-9 



