20 ASTACIDiE. 



[owing exactly the outside suture. The size of this corneous cone, and 

 the shape of the suture and apical hole, differ considerably in the differ- 

 ent species, and seem, to some extent, constant in the same specie-;. 

 The structure and shape of this organ seem to be for some sexual 

 purpose. The ridges (in 0. aetdus, Glarkii, Bartonii, etc.) have an inner 

 open entrance on the front margin, and seem opened between the suture 

 outside on the hind margin. In the annulus I found fat and fibrous 

 matter imbedded, and perhaps a glandular mass, which it was not easy 

 to determine in the old alcoholic specimens. Nevertheless, the whole 

 apparatus seems to be fitted for some secretion. Tab. II. f. 127. 



The corneous cone in the species of Gambarus is well separated from 

 the ventral plate, being only united to it by a membrane, movable in 

 the young and sometimes even in the full-grown individuals. This is a 

 specific character ( C. troglodytes). 



In the true Astacus this organ exists; still it is not separated from the 

 ventral plate, except by an external channelled space ; it forms a slen- 

 der transverse ridge, varying in shape in different species, but not so 

 conspicuously, and baving no denticulated suture or secretional apparatus. 



I have sometimes thought that this apparatus might perhaps serve 

 for gluing the eggs to the abdominal legs ; but as this does not exist in 

 the true Astacus, it seems improbable. By what is possibly a singular 

 coincidence, I have failed to find, among specimens from more than 

 thirty localities and among several hundred females of all sizes, a single 

 female, in the Cambari of the group C. aetdus, with the eggs attached. 

 Two females have young between the abdominal legs, but no remains 

 of the egg-cases. Do the females of the group of C. aetdus lay their 

 eggs in a manner different from the other Cambari? I presume not. 



■Eggs: their Attachment and Bursting. — The eggs in the Astacidae are 

 always attached, as in some insects (in Chrgsopa, Hemerobius, Mantispa), 

 by a short stem. Before the appearance of the egg the glue is excreted 

 from the female sexual aperture, fixed, and drawn out into a stem ; 

 finally the egg is tixed upon it. It is also to be presumed that the 

 Astacidae fix their eggs in the same manner. I should remark that the 

 stem in the Astaci is always much stronger than in the Cambari. 



It is, perhaps, interesting to notice that the eggs in the true Astacidaa 

 are always burst in the same manner, viz. into two parts perpendicu- 

 larly, the segments remaining attached to the stem. This condition 

 makes its probable that the Astacus embryo has a particular egg-burster 

 similar to that in the insects, although these interesting parts are little 

 observed or. known even by entomologists. 



Development of the First Pair of Abdominal Legs in the Mule — It is easy 

 to discriminate between the sexes of very young individuals of Gam- 

 barus Clar/cii. This is the case with those only 0.3 inch long, and 

 while they still occupy the postabdomen of the mother. In the females 



