16 PHYSIOLOGICAL SERIES. 



their posterior halves being left in front of the segment, 

 their anterior behind. On the left side the anterior half of 

 the endopleurite is painted light blue, the posterior dark. 

 The endosternites are similarly treated with red. 



A. 52. Entosternite of Apus productus. It is attached by 

 muscles to the cuticle of the body-walls, and lies between 

 the nervous system below and alimentary canal above. It 

 has the structure of fibro-cartilage. The entosternite is 

 thought to be represented in the Lobster by a small thin 

 plate of connective tissue that lies immediately above the 

 expanded inner ends of the first pair of endosternites. 



Presented by H. M. Bernard, Esq. 

 Ray Lankester, Q. J. Micr. Sci., vol. xxiv. 1884, p. 131. 



A. 53. Entosteruite of King Crab (Limulus polypliemus] . It 

 has the same general structure and position as the former 

 specimen. In chemical composition it consists of a 

 chondrin-like body, and chitin (I'Ol %). 



Presented by M. F. Woodward, Esq. 

 Halliburton, Q. J. Micr. Sci., vol. xxv. 1885, p. 179. 



ARACHNIDA. 



A. 54. Entosternite of a Scorpion (Palamnceus spinifer). It 

 has the usual minute structure and composition of that 

 of other Arthropods. It consists of a stoutish body 

 situated in the thorax between the alimentary canal and the 

 nervous system, and of two " posterior flaps " or wings that 

 extend upwards and backwards, having the position of a 

 diaphragm situated at the junction of the cephalothorax and 

 abdomen. 



Schimkewitsch, Zool. Jahrb., Bd. viii. 1895, p. 191. 



A. 55. Entosternite, together with the ventral plate (sternum) 

 and proximal portions of the limbs of a Spider (Ihera- 

 phosa blondii}. The entosternite was loosely attached to 

 the sternum by three pairs of slender processes. It gave 

 attachment to numerous muscles. 



