On the Structure and Development of Argiope. 



By 

 Arthur E. Shipley, 



Scholai of Ghrist's College, Cambridge. 



With Plates 39 and 40. 



The two species of Argiope, which I bave studied at the Zoological 

 Station Naples, occur at a depth of atout 70 metres in the Bay of 

 Naples. They diflfer considerably in their appearance. The shell of A. 

 neapolitana (tìg. 9) is of a uniform brownish white color, studded 

 with numerous white spots , due to the presence of the canals which 

 perforate the shell. The ventral shell is heart shaped, its posterior end 

 is pointed, forming the beak. the anterior end is broad and has a median 

 depression. The greatest length of this shell is from 2.5 to 3 mm, the 

 greatest breadth which is about one third of the length from the ante- 

 rior border is about the sanie. The aperture through which the stalk 

 passes is not completed by the ventral shell, but the anterior side is for- 

 med by the posterior border of the dorsal shell. The remaining three 

 sides of the aperture are formed by the ventral shell , the posterior by 

 the posterior apex, and the sides by the inner borders of two triangulär 

 areas which belong to the sanie shell but are bent under to lie in the 

 same piane as the dorsal shell 'fig. 1 7 ir) . The apex of this triangulär 

 area bears a tooth-like process which fits into a socket on the dorsal 

 shell. There is a slight median ridge which runs from the posterior of 

 the ventral shell for about two thirds of its length on its inner side, 

 dividing the shell into two equal halves (fig. 17 tv). 



The dorsal shell is not seen when the animai is in its naturai po- 

 sition, It is not so vaulted as the other, but in outline it resembles it, 

 only instead of ending in a point, the posterior third is cut away. The 

 posterior border may be divided into three parts, the centrai third for- 

 ming the anterior border of the aperture through which the stalk passes, 



