ME. R. M'laCHLAN ON IHE NYMPH-STAGE OP THE EMBID.E. 373 



ments more or less with age by the ankylosis of the sacral vertebrae, 

 so as not to render the extent of the " sacrum " very variable. It 

 would surely be well, then, to distinguish the human sacral ver- 

 tebrae, like the ribs, into true and false, those being the true 

 sacral vertebrae which abut*against the ilium. 



In Birds the determination of the homological relations of the 

 different parts of the postdorsal part of the spinal column is a 

 matter of much difficulty. On the whole, and seeing on the 

 one hand the manifest homology between the sacral vertebrae of 

 Man and Lizards by the help of Crocodiles and Tortoises, and on 

 the other hand the manifest homology between the sacral vertebra9 

 of Lizards and the posterior parapophysial vertebrae of most Birds, 

 the authors think it better to regard the latter vertebrae in Birds 

 as alone truly sacral, and to regard sucli forms as Buceros, Pica, 

 and certain Parrots as differing from the rule of the Glass in the 

 suppression of their parapophysial processes, axidiFregatta as differ- 

 ing from the same rule by the development of parapophyses in all 

 the vertebrae of this region. 



The sacral vertebrae in Birds may be defined, then, as " ver- 

 tebrce Jiaving one of the more postaxial roots of the sciatic plexus 

 coming forth either immediately preaxiad or postaxiad, and having 

 parapophysial transverse processes abutting against the ilium, such 

 vertehrce heing placed immediately postaxiad to vertehrce which are 

 devoid of such parapophyses, or else heing the homologues of a ver- 

 tebra so conditioned in most birds. 



By the combination of these two definitions, as given above 

 (the one for Mammals, Eeptiles, and Batrachians, and the other 

 for Birds), it seems to the authors tliat the sacral vertebrae may 

 be defined in all Vertebrata above Fishes which have pelvic limbs. 



On the Nymph-stage of the Embida, with notes on the Habits of 



tlie Family, &c. By E. M'Lachlaj^, Esq., F.E.S., F.L.S., &c. 



[Eead June 7, 1877.] 



(Plate XXI.) 



Introductory RemarTcs. 



In the year 1837 Prof. Westwood published in the ' Transactions ' 



of this Society (vol. xvii. pp. 369-375, pi. xi.) a memoir entitled 



" Characters of Embia, a Genus of Insects allied to the White ' 



Ants ; with descriptions of the species of which it is composed," 



wherein he gave a resume of the little hitherto known concerning 



