148 Mr. G. Newport on the Reproduction 



femur, tibia, tarsus and claw, as well as rudiments of spines 

 (PL VIII. fig. 2). It thus agrees precisely with the new limbs 

 produced in Lepidoptera. I have found in every instance in my 

 experiments that all the primary or essential parts of a limb exist 

 when the new organ first makes its appearance; but that its se- 

 condary parts, as, for instance, the armature of spines and the 

 joints of the tarsus, are later in their formation. The joints of 

 the tarsus usually are fewer in number in new limbs that have 

 not attained the normal size than in the original limbs. This is 

 invariably the case when the limb is first produced. As the en- 

 tire organ continues to grow, the tarsus becomes more and more 

 elongated, proportionately to the other parts ; and when the insect 

 next changes its tegument, the number of joints to this part 

 of the limb is increased by the production of a new joint at the 

 distal extremity of the penultimate one, interposed between it 

 and the joint which bears the claw ; precisely as new segments are 

 added to the body of the Myriapod, between the last newly-pro- 

 duced segment and the caudal, or penultimate, at each change of 

 its covering. It is in this way also that new joints are developed 

 in the antennse of Lithobius, always at the distal margin of a pre- 

 existing joint, only that in this case the new part is formed at 

 the distal end of each previous joint. 



In the specimen of Panesthia above alluded to, there are only 

 three joints to the tarsus, instead of five, besides the unguis. Of 

 these, the basilar or true tarsal joint, as in the perfect limb, is the 

 longest, so that those joints which are nearest to the body are 

 always, at first, most quickly enlarged and elongated. Thus, as 

 the growth of the whole limb proceeds, first the femur and next 

 the tibia become proportionately elongated, and lastly the tarsus 

 and its subdivision into joints. This is a fact of some import- 

 ance in a comparative anatomical and zoological point of view, 

 because it shows that an increased number of tarsal joints 

 amongst true insects is not a proof of inferior development. 



The immediate source of origin of the new limb is extremely 

 difficult to ascertain. My own experiments on Lepidoptera, and 

 Mr. Goodsir's on the Crustacea, lead to the belief that the new 

 limb has its origin in a little, elevated, central point, beneath the 

 cicatrix which covers the surface of the space to which the old 

 limb was attached ; and that within this little elevated point, as 

 within a capsule, the microscopic rudiments of the new limb are 

 formed. Mr. Goodsir^s observations on the Crustacea seem to 

 show that even at this early period the limb is formed of distinct 

 articulations ; but recent observations made by myself on the 

 original formation of the limbs in the Chilopoda and in the For- 

 ficulidoi have led me to believe that this is not the case in the 

 earliest state of the limbs in the Myriapoda and in these insects, 



