INVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 617 



sometimes show circles of dried blood round the stigmatic opening. 

 But the stigmata which are thus shown to open under certain con- 

 ditions can hardly be closed by any other than mechanical means ; 

 for it is impossible that their walls, lined as they are by a continua- 

 tion of the cuticle, can fuse together as has been stated. The reason 

 that the stigma of the first of the eight abdominal segments is so often 

 overlooked, is that in the exuvium its tracheal branch lies immediately 

 under the longitudinal cord, composed of the aggregated tracheae ; it 

 is smaller in the imago of ^schna constrida than in the larva. 



A muscular apparatus, at any rate in the second and the other 

 posterior segments of the larvae, passes backwards and upwards from 

 the stigma in a groove to the internal angle of the segment. The 

 prothoracic stigmata differ from those of the abdomen in having 

 the appearance of an actively used apparatus ; a number of large well- 

 developed tracheae pass directly to the stigma, within the two lips of 

 which their openings — covered by a membrane containing a dense 

 reticulum of quadrangular cells, as in the Perlidae — are readily to be 

 seen ; the commencement of the spiral thread in the form of folds. 

 The mesothoracic stigma is closed by a plate which is externally 

 clothed with hair ; in the larva this plate carries epidermis as 

 well, and constitutes the " tympanum " of Oustalet ; the tracheae 

 appear to be functionally active here also, though less so than in the 

 prothoracic. The tissues of the tracheal brancheae of the rectum are 

 cast ofi' in Ejjitheca bimaculata and prince'ps, and not renewed in the 

 imago — they are 5 * 5 mm. long in this genus ; the same seems to hold 

 with other genera, though it is the exception in ^sclina. 



Although it has been contradicted, the respiration in the larvae of 

 Calopteryginae is conducted by a tracheal system distributed in three 

 rings which surround the rectum. The middle foliar gill is supplied 

 by tracheae. Euphcea manifests a still higher development in the 

 possession of long conical organs on both sides, like those of Sialis, 

 seen in E, sjAendens and a species from Ceylon. In some larvae 

 (probably belonging to a new species, to be called Aniso'ptertjx comes, 

 from the Himalaya), a long pointed cone of cuticular structure extends 

 along each side of the body from the second to the eighth segment ; the 

 caudal branchiae are inflated and pointed, each inflated mass contains 

 a fat body externally pigmented and supplied richly with tracheae 

 internally ; a tube of similar dark colour and structure extends into 

 the lateral respiratory cone. On the front edge of the eighth external 

 plate in Ejritheca and Libcllnla occurs an oblique slit "5 mm. long, 

 leading into a sac in the body which is loosely enveloped by another 

 sac of the shape of a Phrygian cap, and • 5 mm. long by • 5 mm. broad, 

 the inner one being covered with pavcment-ei^ithclium ; outside this iu 

 the articulation fold of the segment is an area covered with similar 

 cells ; the external loose sac, like the ci)idermis of a large traclical 

 stem, shows rows of fine granules imdcr a high power. Tracliero wcro 

 traced to the slit or opening. This apparatus lias not been found iu 

 the Agrionidao. It may possibly secrete a lubricating substance for 

 the joints, and pcrliaps is connected morphidogically with the 

 abdominal appendages, which are present in Euphiva. 



