70 THE MICROSCOPE AND ITS REVELATIONS. 



tabulation or non-tubulation of Foraminiferal shells is the key to a very 

 important Physiological difference between the Animal inhabitants of 

 the two kinds respectively; for whilst every segment of the sarcode-body 

 in the former case gives off pseudopodia, which pass at once into the sur- 

 rounding medium, and contribute by their action to the nutrition of the 

 segment from which they proceed, these pseudopodia are limited in the 

 latter case to i\\Q final segment, issuing forth only through the aperture 

 of the last chamber, so that all the nutrient material which they draw-in 

 must be first received into the last segment, and be transmitted thence 

 from one segment to another until it reaches the earliest. With this dif- 

 ference in the physiological condition of the Animal of these two types, 

 is usually associated a further Tiery important difference in the conforma- 

 tion of the Shell viz., that whilst the aperture of communication be- 

 tween the chambers, and between the last chamber and the exterior, is. 

 usually very small in the ' vitreous' shells, serving merely to give passage 

 to a slender stolon or thread of sarcode from which the succeeding seg- 

 ment may be budded-off, it is much wider in the ' porcellanous ' shells, 

 so as to give passage to a ' stolon' that may not only bud-off new seg- 

 ments, but may serve as the medium for transmitting nutrient material 

 from the outer to the inner chambers. 



461. Between the highest types of the Porcellanous and the Vitreous 

 series respectively, which frequently bear a close resemblance to each 

 other in form, there are certain other well-marked differences in struc- 

 ture, which clearly indicate their essential dissimilarity. Thus, for ex- 

 ample, if we compare OrUtolites (Fig. 316) with Cycloclypeus (Plate xvi., 

 fig. 1), we recognize the same plan of growth in each, the chamberlets 

 being arranged in concentric rings around the primordial chamber; and 

 to a superficial observer there would appear little difference between 

 them. But a minuter examination shows that not only is the texture of 

 the shell ' porcellanous ' and non-tubular in Orbitolites, whilst it is * vit- 

 reous ' and minutely tubular in Oycloclypeus; but that the partitions be- 

 tween the chamberlets are single in the former, whilst they are double in 

 the latter, each segment of the sarcode-body having its own proper shelly 

 investment. Moreover, between these double partitions an additional 

 deposit of calcareous substance is very commonly found, constituting 

 what may be termed the intermediate skeleton; and this is traversed by a 

 peculiar system of inosculating canals, which pass around the chamber- 

 lets in interspaces left between the two laminse of their partitions, and 

 which seem to convey through its substance extensions of the sarcode- 

 body whose segments occupy the chamberlets. We occasionally find this 

 ' intermediate skeleton ' extending itself into peculiar outgroioths, which 

 have no direct relation to the chambered shell; of this we have a very 

 curious example in Calcarina (Plate xvi., fig. 3); and it is in these the^ 

 we find the ' canal-system ' attaining its greatest development. Its most 

 regular distribution, however, is seen in Polystomella and in Operculina; 

 and an account of it will be given in the description of those types. 



462. PORCELLANEA. Commencing, now, with the Porcellanous se- 

 ries, we shall briefly notice some of its most important forms, which are 

 so related to each other as to constitute but the one family Miliolida. Its 

 simplest type is presented by the Cornuspira (Plate xv., fig. 1) of our 

 own coasts, found attached to Sea-weeds and Zoophytes; this is a minute 

 spiral shell, of which the interior forms a continuous tube not divided 

 into chambers; the latter portion of the spire is often very much flat- 

 tened-out, as in PeneropHs (fig. 5), so that the form of the mouth is 



