112 MANUAL OF HISTOLOGY. 



0-0050-0-0043 mm. (in the hen). The nucleus usually occupies the 

 middle portion of the cell, but lies occasionally excentric. 



Again, we find the blood-cells of scaly amphibia, of tortoises, lizards, 

 and snakes, also oval, but somewhat broader and longer than those of 

 birds. In length they range from 0-0182 to 0*0150 mm. ; but the central 

 boss is somewhat less prominent. The cells of the osseous fishes also are 

 small, and bat slightly oval (fig. 113, 7, a a 5), measuring O'0182-O'OIH. 

 In the naked amphibia and fishes with transverse mouth, the oval or 

 elliptical blood-corpuscles show the most astounding dimensions. The 

 length of those of rays and sharks is 0-0285-0-0226 mm. ; of toads and 

 frogs (fig. 113, 6, a a &), on an average 0*0226 mm.; of tritons 

 (fig. 113, 5, a a &), '0325-0 -02 25 mm. ; and of salamanders, 

 0-0445-0-0375 mm. The diameters of the cells of the ichthyoida (Fisch- 

 lurche) are even considerably larger, so that a powerful eye can just recog- 

 nise them, without a microscope, as minute dots ; as, for instance, in 

 the cryptobranchus, in which their length is 0'0510 mm., and proteus 

 (fig. 113, 4), where they are 0*0570 mm. 



.Finally, the cyclostomata (fig. 113, 8) possess, as we have already 

 remarked, red cells, having the form of small round 

 biconcave disks (b) with a diameter of about 0-013 mm. 

 All these cells conduct themselves towards reagents 

 in a similar manner to those of man ; but many of the 

 FI in TWO bio< effects produced on them are naturally clearer and 

 ceils from the fro^. sharper owing to their larger proportions. In this 

 nudei w as th thly a come respect the corpuscles of the frog may be particularly 

 to view under the noticed as objects easily procurable for first observa- 

 tions ; in them the nucleus can be rendered visible 

 in a moment by the addition of water (fig. 114). 



The bodies of these cells may possibly contain a certain amount of 

 protoplasm, but a membrane is certainly not present on the greater 

 number of the corpuscles of frog's blood, as the spherical segmentation 

 observed among them seems to indicate : Rolletfs discovery also, that two 

 cells may coalesce to form one spheroidal mass, on being subjected to a dis- 

 charge of electricity, would lead to the same conclusions. Some isolated 

 cells, however, of frog's blood (possibly senescent) do possess a distinct 

 membrane. 



REMARKS. 1. Comp. Besides R. Wagner's works, which opened the way to farther 

 discoveries (Beitrage zur vergleichenden Physiologic des Blutes, Leipzig, 1833 ; und 

 Nachtrage, Leipzig, 1836. Gulliver (Proceedings of Zool. Society, 152, 1842). 

 2. The Amphiuma tridactylum has, according to Riddel, the largest of all blood-cells, 

 exceeding those of the proteus by a third. (New Orleans, Med. and Surg. Journ., 

 1859. January). 3. Comp. Robert's in. ihe Quart. Journ. of Microscop. Science, 1863, 

 Journ. p. 170. 



69. 



Whilst the coloured blood-corpuscles present in beings of the same 

 kind the greatest uniformity and correspondence (with the exception of 

 those extraordinary typical deviations in the vertebrates), and must be 

 looked upon as the fully developed and completed cells of the blood, 

 which undergo no further kind of perfecting in the system, but rather 

 decay at a later period by rupture and solution, the nature of the second 

 cellular element of this fluid, namely, the colourless blood-cell or so-called 

 lymph-corpuscle (lymphoi-d cell), is completely different. We have here 



