ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 711 



Leydig knows of several cases in which whole cells have become cuticu- 

 larized, and cites the jaws of Paludina, Ancylus, and Lymnseus. 



In treating of the tissues, Prof. Leydig deals with some recent 

 remarks of Dr. H. Eisig. As to the mode of origin of the cuticular 

 fringe, it is to be observed that, as long as the cell-substance was regarded 

 as a homogeneous mass containing granules, the fringe could only be 

 regarded as a secretion of the matrix-cells ; but when the difference 

 between hyaloplasm and spongioplasm was recognized, the question arose 

 — Is the cuticle formed by the hyaloplasm only, or does the spongioplasm 

 take any share in it ? The author believes that both take a part, but 

 the cardinal point is that the cuticular substances are formed by the 

 secretory and metamorphic activity of the matrix-cells. Eisig's view 

 that the cuticle is formed by agglomeration of rod-like structures formed 

 by glandular cells may be shown to be erroneous by the following obser- 

 vations : — In some German Gastropods peculiarly-formed corpuscles are 

 to be found in the dermal glands, and the byssus, and the " bloom " on 

 some shells, as well as the powder of some insects, are all formations of 

 dermal glands, yet they never take any part in giving rise to the fibrous 

 differentiation of the cuticle. 



Prof. Leydig is of opinion that cuticular tissue is allied to connective 

 tissue. This view is based on a number of observations : — 



(1) The cuticular tissue forms the hard or skeletal parts of Arthro- 

 pods (dermal carapace as well as skeletal parts), and represents therefore 

 the tissue which takes its place in Vertebrates. 



(2) In the form of their early development the cuticular tissue of an 

 Arthropod and the connective tissue of a Vertebrate agree ; in both cases 

 it consists of matrix-cells and an overlying layer of homogeneous sub- 

 stance. Sarcolemma or neurilemma or the corium of a Batrachian larva 

 present the same characters as the cuticular tissue of an Arthropod. 



(3) The cuticular tissue of the integument is in Arthropods con- 

 nected uninterruptedly with the connective tissue of the interior of the 

 body. 



(4) When the minute structure of cuticular tissue, especially that of 

 the dermal carapace of Arthropoda, is compared with the connective 

 tissue of Vertebrates, we find in both striated homogeneous layers and 

 parts condensed into fibres, and in both cases there is a traversing system 

 of lacunae, clefts, and pore-canals. 



While some recent authors have taken different views as to the struc- 

 ture of the dotted substance of Vertebrates from those held by Leydig, 

 it has been a matter of satisfaction to him that the most exact (Nansen) 

 holds his doctrine. He does not doubt that Hansen's explanation of the 

 dotted substance as a thick plexus of very fine nerve-tubes is correct. It 

 is clear from Leydig's earlier observations that we ought to speak of the 

 nerve-tubes rather than the nerve-fibres of Annelids and Arthropods. 

 In these tubes one may distinguish a spongioplasm, which forms the 

 investment, and the hyaloplasm or inclosed soft and semi-fluid nerve- 

 material. The former may be continued inwards as a framework. The 

 nerve-fibres of Vertebrates also ought to be called nerve-tubes and not 

 fibres, and in them there appear to be at least remnants of an internal 

 meshwork. Here again the author finds matter for criticism in Eisig's 

 latest work. 



The hyaloplasm ought to be regarded as the " primum agens " in the 

 nerve-tissue. Leydig has spoken of the spaces in the spongework as an 



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