374 HISTOLOGY 



points which loose their own epithelial covering, but succeed in preserv- 

 ing that of the wider surfaces which lie between them. 



The shape of these plates varies exceedingly. Some are flat and 

 hard. Others are spongy in texture, while in the Holothuria they form 

 isolated plates of various patterns, some of them very beautiful, as the 

 anchor plates in some of the Synaptas. 



Technic. The technic of this group of tissues varies from the sim- 

 plest and easiest to the most difficult, mechanically, owing to the great 

 variety in which the protective substances and cells are developed. The 

 difficulty lies in the hardness of these parts, and the consequent breaking, 

 irregularity, and unmanageability of the sections. The heterogeneous 

 tissues are the worst in this respect. The remedy in most cases is an 

 extra sharp and good knife, and a deliberate and careful handling of 

 the sections when they have been secured. In case the hardness is due 

 to some salt of lime, the tissue should be decalcified either by the fixative 

 or by a subsequent treatment with hydrochloric acid and phloroglucin. 

 When it is due to chitin and connective-tissue substances the problem 

 is not so easy. Most methods of softening these materials injure the 

 structure and staining power. It is therefore better to use such processes 

 only as a last resort and to first try to get sections with a very good knife 

 by the ordinary way. Sometimes it is best to saw off thick sections and 

 then to grind them down on a stone in oil. If soft parts are associated 

 with the hard parts and must be preserved, the whole mass must be 

 fixed and then embedded in rosin, in which condition the entire structure, 

 soft and hard alike, may be sawed off and ground and then mounted after 

 the rosin has been dissolved. In some instances teasing of fresh or fixed 

 material and hand sections of fresh material will give good results after 

 all other methods have failed. 



LITERATURE 



But few papers deal with the integument as a whole. Accounts of this organ usually 

 form parts of more general descriptions or articles based upon researches that have been 

 made on some particular component tissue of the integument. Papers and descriptions 

 may be found in the following places. 



SCHNEIDER, K. C. "Lehrbuch der vergleichenden Histologie," Jena, 1902. 

 HALLER, B. "Lehrbuch der vergleichenden Anatomic," Jena, 1904. 



Read parts of Parker and Haswell, Lang, and other Zoologies. Accounts of the skin 

 in medical histologies. 

 BLASCHKO, A. "Beitrage zur Anatomie der Oberhaut," Arch.f. mik. Anat., Band XXX, 



S. 498, 1887. 

 CERFONTAINE, P. " Recherches sur le Systeme cutane" et sur le Systeme musculaire du 



Lombrie terrestre," Arch. Biol., Band X, 1890. 

 TOLDT, C. "Uber den feineren Bau der Cuticula von Ascaris megalocephala," Arb. Z. 



Inst. Wein, Band XI, 1899. 

 BIEDERMANN, W. " Untersuchungen iiber Bau und Entstehung der Molluskenschalen," 



Jen. Zeits. naturwiss., Band XXXVI, 1901. 



