1918.] NATURAL SCIENCES OF PHILADELPHIA. 93 



p. 82, Fig. 1). They resemble more the folds seen in Argia moesta 

 putrida (Cullen, I.e.) The epithelium, too, is much thicker (41 to 83 m) 

 in Mecistogaster modestus than in the first two larvae named above, 

 resembling more Argia moesta putrida in this respect also. But on 

 slide 7 of Thaumatoneura larva No. 7 (female, Dr. Calvert's parsonal 

 collection), I found sections where the epithelium of the rectal folds 

 was about as thick (50 or 60 m) as that of the corresponding region 

 in Meeistogaster.^ 



About section 310 (Fig. 6) the three folds (4, 8, 12) of thick 

 columnar epithelium begin to occupy less, and the pigmented areas 

 separating them more, of the gut wall. At section 370 the folds 

 (or rather bands, for they are no longer folds) of columnar 

 epithelium have contracted so as to form only about half of the gut 

 wall. The epithelium of these bands has, however, become much 

 thicker (83/>-) than further cephalad. Between these bands are 

 seen three folds (Nos. 2, 6 and 10) of spongy or reticulate connective 

 tissue covered on the lumen side by the more or less broken down 

 epithelium of the pigmented areas mentioned above. While spaces 

 filled with blood and an occasional jMalpighian tubule exist between 

 the basement membrane of folds 4, 8 and 12 and the circular muscle 

 coat, the circular muscle fibres are in contact with the spongy tissue 

 of folds 2, 6 and 10. 



Folds of spongy tissue, homologous to those in Mecistogaster, 

 occur in the rectum of Thaumatoneura larva. On slide 7 of Thauma- 

 toneura larva No. 7, female, (Dr. Calvert's collection), there are 

 three such folds of reticulate tissue covered by a pigmented 

 epithelium. 



About section 373 (Fig. 6) some of the spongy tissue extends 

 out into the hsemocoele. 



From section 383 (Fig. 6), anterior part of segment X, caudad 

 to the end of the gut no more is seen of the large columnar cells of 

 the longitudinal folds. This region, from about section 380 to the 

 end of the gut, corresponds to the vestibule or anal part of the 

 rectum of Anisopterous larvae (Sadones, 1895, pp. 277, 280, 315; 

 Tillyard, 1916, p. 131 and 1917, pp. 101, 114, 115, 116; Faussek, 

 1887, p. 45). But there are not two kinds of epithelia as described 

 by Sadones for Libellula depressa, nor is there any indication of a 



(^ As the larvae of Thaumatoneura and of Argia talamanca figured in the 

 papers above cited were unavoidably those which died in attempted rearing, 

 it is perhaps not impossible that the thinness of their epithelia may be a 

 starvation effect. — P. P. Calvert.) 



