ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 561 



colour differences are seen in any part of the crab except upon the 

 first pair of appendages, and it is interesting to note that this sexual 

 difference does not make its appearance till the crab reaches maturity. 

 The chel« of immature males and females cannot be distinguished 

 from each other. Fritz Miiller says that the same is true of the 

 Gelasmus species observed by him. On the other hand, considering 

 the habits of Crustacea, these sexual differences can hardly be 

 considered as the results of sexual selection. 



Observations on Tanais cerstedi.* — H. Blanc takes Tanais as his 

 text for a study of the cliaracters of the heteropodous Asellidaa. Com- 

 mencing with a general account of the body and its appendages, he 

 states that the differences between the cephalothorax of the male and 

 female are not so well marked in young examples, and are not at all 

 apparent io embryos. In old specimens the chitinous integument is 

 incrusted with calcareous salts, which have the form of small masses, 

 crystalline in structure, which may be either needle-shaped or rounded. 

 The concretions are altogether similar to those found by Hoek in the 

 Caprellidae, and the differences in their form are due to the presence 

 or absence of a hypodermic nucleus. The tegumentary glands 

 are represented by three pairs of large glands which are placed 

 beneath the lateral integument of the first three free segments of 

 the thorax, and by twelve pairs of glands, which are much smaller 

 than the others and are placed in the lateral portions of all the 

 thoracic and abdominal segments, and in the head. The former 

 are racemose in structure and closely resemble the same organs 

 in Phronima, Hyperia, and Corophium. Each element of the racemose 

 glands is formed of a mass of ju-otoplasm, which contains two 

 very clear nuclear vesicles, each of which is nucleolated. Each 

 vesicle is, therefore, formed of two cells. The secretion from these 

 cells passes out by small unbranched canaliculi, to reach the exterior by 

 a single canal. The large thoracic glands are best developed in 

 females carrying embryos in their incubatory pouches, and in them 

 the glandular elements have their protoplasm almost entirely converted 

 into a secretion. The product secreted hardens in the water and so 

 forms a tube into which the Tanais may retreat ; when fresh, and to the 

 naked eye, this secretion appears to be filamentous ; but when examined 

 under the Microscope, it is seen to be composed of small rod-shaped 

 corpuscles similar to those contained in the glandular elements. The 

 secretion is more colloid than mucilaginous, for it does not coagulate 

 with alcohol or form an emulsion with olive-oil. The secretion of the 

 smaller pyriform glands probably has the function of secreting a 

 product which prevents the animal from drying completely when it 

 happens to float on the surface of the water. 



The supra-cesophageal mass is elongated in the male, and short, 

 widened out laterally in the female. It is distinctly divided into a 

 superior optic portion and an inferiorly placed part which is larger 

 and ffirruH the true cerebrum. The differences between the supra- 

 ctsophageal ganglia of the male and female arc carefully pointed out. 



♦ Recueil Zoo). Suisse, i. (1884) pp. 189-258 (3 pie.). 



