ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 653 



demonstrate the constant possession of a chitinogenous layer, and the 

 homology between the integuments of Crustacea and those of higher 

 animals; there is a definite separation into dermis and epidermis. 

 He has also been enabled to detect a close connection between the 

 formation of fresh integuments and an abundance of glycogen. 



The " first part of the epidermis " consists of a cuticle, a pigmented 

 layer formed of parallel lamellte traversed by canaliculi, a calcified 

 layer, which forms by far the greater part of the carapace, and a non- 

 calcified layer formed of very small lamellfe; the " second part" is 

 represented by the cylindrical epitheliimi, which is the representative 

 of the Malpighian layer of higher forms. 



At the moment of ecdysis the new coverings of the crustacean are 

 not completely formed, though one may distinguish all the difterent 

 layers of chitine which can be made out in a well-formed integu- 

 ment ; in the crayfish, at this moment, we may see, in sections, the 

 old carapace, the new carapace, the chitinogenous epithelium, and 

 the layer of connective tissue. The most remarkable character 

 appears to be the constant presence of the third or chitinogenous 

 layer, which is formed of large, more or less cylindrical cells ; in the 

 imderlying tissue vessels and nerves are to be detected, and it, there- 

 fore, is truly a dermis, while all that lies outside it is epidermal. In 

 the ecdysis it is only the outer layers of the epidermis that are cast 



The author then proceeds to an account of the chitinous lining of 

 the digestive tract, which presents a similar history to the external 

 investment. As Max Braun was the first to point out, glands, which, 

 from their position may be called salivary, are really present in the 

 higher Crustacea; glands of exactly similar structure to those of the 

 oesophagus are to be found in the intestine, and the author has con- 

 sequently some difficulty in forming an hypothesis as to their 

 function. 



The chitinous layers have a cellular origin, and this stratum of 

 cells becomes of great size diu'ing the ecdysis, and diminishes again 

 after the formation of the chitinous layers; but the diminution in 

 length is not proportional to the thickness of the new layers, for it is 

 compensated for by tbe using up of the glycogenic material which is 

 contained in the large cells of the connective tissue. The process of 

 growth in the integument is not due to the secretion of a chitinous 

 material from the cells of the chitinogenous epithelium, but to the 

 successive thickening of the superior portion of the cells which separ- 

 ates from the body of the cell ; herein we find the explanation of the 

 constitution of the integument by parallel lamellae. Growth of the 

 individual appears to take place before and not during the ecdysis. 



The presence of glycogen and its origin is discussed, and it is 

 finally regarded as being a reserve of organic material primarily due 

 to a slowing of the processes of nutrition during winter and early 

 spring ; the term of " reserve of inorganic material " is applied to such 

 calcareous concretions as the gastroliths of the crayfish. The author 

 has borrowed many of the excellent illustrations which adorn Prof. 

 Huxley's book on the crayfish. 



Ser. 2.— Vol. III. 2 X 



