CHAP. II.] SEGMENTS OF ARTHROPODA. 93 



NEOTROPICAL SPECIES. 



In all the Neotropical Species which have been at all fully ex- 

 amined, the number of legs varies among individuals of the same 

 species. 



P. edwardsii: number of pairs of legs variable, the smallest 

 number being 29 pairs, and the greatest number being 34. Males 

 with 29 and 30 pairs of legs. The females are larger, and have a 

 greater number of legs than the males. 



The new-born young differ in the same way. From 4 females 

 each having 29 legs, seven embryos were taken which were practi- 

 cally fully developed. Of these, 4 had 29 legs, 2 had 34, 1 had 32. 

 An embryo with 29 ami one with 30 were found in the same mother. 

 An embryo, quite immature, but possessing the full number of legs, 

 was found with a larger number of legs than one which occupied 

 the part of the uterus next to the external opening. (Caracas.) 



Peripatus demeraranus : 7 adult specimens had 30 pairs of 

 legs; 6 had 31 pairs; 1 had 27 pairs. Out of 13 embryos ex- 

 amined, 7 have 30 pairs and 6 had 31. (Demerara.) 



Peripatus trinidadensis : 28 to 31 pairs of ambulatory legs. 

 (Trinidad.) 



Peripatus torquatus : 41 to 42 pairs. (Trinidad.) 



Specimens of other less fully known species are recorded as 

 having respectively, 19, 28, 30, 32, 36 pairs of legs, &c. 



In the Neotropical Species, irrespective of the number of legs, 

 the generative opening is placed between the legs of the penulti- 

 mate pair. (SEDGWICK, p. 487.) 



Peripatus (j id if or mis?} from St Vincent: six specimens ex- 

 amined. Of these, 1 specimen had 34 pairs of legs, 2 had 32 pairs, 

 1 had 30 pairs, and 1 had 29 pairs. PococK, R I., Nature, 1892, 

 XLVI. p. 100. 



In connexion with the case of Peripatus, the following evidence 

 may be given, though very imperfect and incomplete. 



2. Myriapoda. CHILOGNATHA. Variation in the number of segments 

 composing the body in this division of Myriapods cannot be observed 

 with certainty ; for it is not possible to eliminate changes in number due 

 to age, nevertheless the manner in which this increase occurs has a 

 bearing on the subject. 



In Julus terrestris the number of segments is increased at each 

 moult by growth of new segments between the lately formed antepen- 

 ultimate segment and the permanent penultimate segment. At each 

 of the earlier moults six new segments are here added: in Blaniulus 

 the number thus added is four, and in Polydesmus? two fresh segments 

 are formed at each of the earlier moults. In. each of these forms the 

 number added is the same at each of the earlier moults. NEWPORT, 

 G., Phil Trans., 1841, pp. 129 and 130. 



CHILOPODA. The number of leg-bearing segments differs in the 

 several genera of Chilopoda, but except in the Geophilidse the number 

 proper to each genus is a constant character. For instance in Lithobius 



