70 THE CONNECTIVE TISSUES, BY A. KOLLETT. 



a plexiform connective tissue, consisting of a simple layer of 

 cells united into a plexus, investing the acini of the salivary 

 and lachrymal glands. 



An investing layer of fusiform cells constituting a perineu- 

 rium may be found also on the peripheric branches of nerves, 

 especially amongst the Batrachia. 



A similar covering is also found in the excretory ducts of the 

 mammary glands and elsewhere. 



The forms of connective tissue hitherto described are distinct 

 from the fibrillar connective tissue which is so frequently found 

 in the adult organism. In this, the connective tissue fibrils, 

 which are so well characterised by their yielding gelatine on 

 boiling, by their unbranched course, their smooth edges, and 

 equal thickness, constitute the essential morphological consti- 

 tuent. It must be admitted, however, that in certain cases 

 transitional forms occur between the fibrillar and the above- 

 mentioned forms of connective tissue. These may be met with 

 in many places, but clearly do not hinder us from admitting 

 that in other places a distinction may be drawn between the 

 two in accordance with the facts already given. Otherwise, 

 the difficulty may easily arise that was frequently observable 

 in the old discussion as to whether the structures under ex- 

 amination should be regarded as connective or as elastic tissue. 



FIBRILLAR CONNECTIVE TISSUE. This is the most widely 

 distributed form that is found amongst the Vertebrata; but it 

 has not been clearly proved whether it occurs amongst the In- 

 vertebrata. The connective tissue which is most similar to the 

 fibrillar connective tissue of Vertebrata is that described by 

 Leydig in the Cephalopods.* According to the same inquirer,-)- 

 a fibrillar connective tissue, very similar to fibrous connective 

 tissue, occurs also in the Echinodermata. Reichert described 

 as belonging to connective tissue, certain tissues found in 

 Arthropods, Molluscs, and Yermes. No evidence, however, is 

 furnished, that these tissues are gelatine yielding. Several of 



* Muller's Archiv, 1854, pp. 303 and 310. 

 f Loc. cit. 



