1 66 DESCRIPTIONS OF PREPARATIONS. 



new cuticle, &c. The barbs, when present, are first formed, then the walls of the 

 stem, both alike from the papilla and the walls of the tube. The tip of the hair is 

 slightly hooked, and fits into the pore-canal of its predecessor. When the old 

 integument is cast off the new hairs are therefore evaginated mechanically. The 

 soft substance contained in the stem atrophies and a new hair-papilla is formed, as 

 is believed by Braun from the walls of the tube. 



The glands of the integument are (i) the glands of the roof of the branchial 

 cavity, and (2) the cement glands found only in the female. The former were dis- 

 covered by Leydig. They lie in the substance of the branchiostegite and open 

 singly on the roof of the branchial cavity. They are tubular in structure and are 

 but slightly lobed. The gland cells are columnar and pointed. The cement glands 

 were discovered and investigated by Braun, and have been found by him in other 

 Decapoda. In the Crayfish they extend over the anterior two-thirds of the ventral 

 surfaces of the abdominal pleura, and thence they spread along the edges of the 

 sterna almost continuously. They also cover about a third of the base of the 

 exo- and endo-podite of the last pair of swimmerets. These cement glands undergo 

 a periodical development, 5-8 weeks before the eggs are laid in November or 

 December, and then they give the parts a whitish appearance. The glands them- 

 selves are tubular with rounded or polyhedric. cells supported by a basement 

 membrane : their ducts rarely open singly, but as a rule in groups. Lereboullet, 

 who first observed the white appearance of the abdomen, but who failed to recognise 

 the glands, states that their secretion coagulates on exposure to water. Shortly 

 before oviposition the female flexes the abdomen ; the cavity thus formed becomes 

 filled with a transparent viscid fluid which glues the edges of the opposing somites 

 together. The ova pass into the chamber, are impregnated and suspended to the 

 setae fringing the abdominal limbs, to the abdominal sterna and intersegmental 

 membranes by a hardened layer of the cementing fluid. It is possible that the 

 fluid may set the spermatozoa free from the coat that binds them together. 



The ectoderm is composed of a single layer of cells columnar or cubical in 

 certain places. In the inner lamella of the branchiostegite, in the abdominal pleura, 

 and the exo- and endo-podite of the last pair of swimmerets, places where the 

 cuticular structures of the two surfaces are near together, the ectoderm cells are 

 enlarged at intervals, and their bases are connected from one to the other surface by 

 bundles of nucleated fibres which appear to be, but are probably not, continuous 

 with the ectoderm cells themselves. A layer of ectoderm cells also intervenes 

 between the attachment of the muscle fibres to their chitinoid, so-called ' tendons,' 

 which are processes in reality of the cuticular structures, and are moulted with 

 them, as has been proved in the case of the tendons of the adductor mandibulae 

 and of the muscle which adducts the dactylopodite of the forceps. 



Beneath the ectoderm is a layer of fibrillated connective tissue, processes of 

 which extend inwards, accompanied by large-celled connective tissue. The pigment 

 cells of this layer are stellate, and contain some a yellow, others a red, pigment, 

 together also with groups of quadrate or oblong crystals of a deep blue colour. Vessels 

 are present, and probably nerves, as irritation of the newly formed integument 

 causes movements on the part of the animal. The moults occur in the warm part 

 of the year (May-September). According to Chantran, they take place (in 

 A. nobilis ?) as follows. The young animal is hatched in May-July. It moults once 



