828 MICKOSCOPIC FORMS OF ANIMAL LIFE 



we see that the segments of the sarcode-body are smooth along their 

 anterior edge b, 6 1 , but that along their posterior edge, a, they are 

 prolonged backwards into a set of ' retral processes ; ' and these pro- 

 cesses lie under the ridges of the shell, whilst the shelly wall dips 

 down in to. the spaces between them, so as to form the furrows seen 

 on the surface. The connections of the segments by stolons, c, c 1 , 

 passing through the pores at the inner margin of each septum, are 

 also admirably displayed in such * casts.' But what they serve most 

 beautifully to demonstrate is the canal system, of which the distri- 

 bution is here most remarkably complete and symmetrical. At d, 

 d l , d 2 are seen three turns of a spiral canal which passes along one 

 end of all the segments of the like number of convolutions, whilst a 

 corresponding canal is found on the side which in the figure is under- 

 most ; these two spires are connected by a set of meridional canals, 

 e, e l , e 2 , which pass down between the two layers of the septa that 



FIG. 626. Internal cast of Polystomella craticulata : a, retral processes 

 proceeding from the posterior margin of one of the segments ; b, b l , smooth 

 anterior margin of the same segment ; c, c 1 , stolons connecting successive 

 segments, and uniting themselves with the diverging branches of the meri- 

 dional canals; d, d l t d 2 , three turns of one of the spiral canals; e, e l , e 2 , 

 three of the meridional canals; /,/ 1 ,/ 2 , their diverging branches. 



divide the segments ; whilst from each of these there passes off 

 towards the surface a set of pairs of diverging branches,/,/ 1 ,/ 2 , which 

 open upon the surface along the two sides of each septal band, the 

 external openings of those on its anterior margin being in the fur- 

 rows between the retral processes of the next segment. These canals 

 appear to be occupied in the living state by prolongations of the 

 sarcode-body ; and the diverging branches of those of each convolu- 

 tion unite themselves, when this is inclosed by another convolution, 



organischen Lebens,' in Abhandhmgen der konic/l. Akad. der Wissenschaften, 

 Berlin, 1855. It was soon afterwards shown by the late Professor Bailey (Quart. Journ. 

 Microsc. Sci. vol. v. 1857, p. 83) that the like infiltration occasionally takes place in 

 recent Foraminifera, enabling similar ' casts ' to be obtained from them by the solu- 

 tion of their shells in dilute acid ; the Author, as well as Messrs. Parker and Rupert 

 Jones, soon afterwards obtained most beautiful and complete internal casts from 

 recent Foraminifera brought from various localities. A number of Greensands yield- 

 ing similar casts were collected on the ' Challenger ' Expedition, the most notable from 

 the coast of Australia. 



