206 M. E. Haase on Abdominal 



glandular cells, immersed like a pocket, and united with 

 retractor muscles and nerves, the efferent ducts of which lead 

 into peculiar hollow capillary processes, so that one is re- 

 minded of the scent-glands of Periplaneta and Corydia ; in 

 Japyx solifugus the glandular mass is simple and less deve- 

 loped. In all species of Japyx there is at the margin of the 

 duplicatuie which represents the rudiment of a leg, and 

 amalgamates with the ventral shield, an unjointed movable 

 chitinous appendage, exactly like an ordinary terminal spur 

 (calcar). 



As in Campodea, there are also in Nicoletia, according to 

 B. Grassi *, ventral sacs and spurs from the second to the 

 eighth abdominal segments; with regard to the important 

 conditions in the first abdominal segment Grassi unfortu- 

 nately says only : — " the false feet, and, I believe, also the 

 vesicles, are wanting." In Lepismina, which, according to 

 Grassi, possesses abdominal spurs only on the three penulti- 

 mate segments, there is on each of the abdominal segments 

 1-8 "a pair of organs comparable with the segmental 

 vesicles" (ventral sacs). In Lepisma the ventral sacs are 

 entirely wanting, while the abdominal spurs may occur from 

 the seventh to the ninth segment. 



The ventral sacs and spurs are most highly developed and 

 have been longest known in the genus Machilis, which was 

 regarded by P. Mayer as particularly near to the primitive 

 insects. The ventral sacs were described as long ago as 1836 

 by Guerin, as delicate, protrusible vesicles at the hinder 

 margins of the ventral plates, which he regarded simply as 

 resembling the branchiae of the lower Crustacea. After the 

 discovery of the tracheae by H. Burmeister and C. T. von 

 Siebold, this interpretation was rejected by the latter, but it 

 has been revived by the most recent investigator, J. T. 

 Oudemans. On the first abdominal segment there is one, on 

 each of the four following segments two, and on each of the 

 others a pair of delicate membranous sacs of considerable size, 

 which are protrusible by the inflow of blood. They are 

 covered with a transparent, perfectly smooth and solid 

 chitinous cuticle, the partly glandular matrix-layer of which 

 contains distinctly limited, flat cells with large nuclei, and 

 they have their own nerves and strongly transversely striated 

 retractor muscles ; tracheae never enter them. On the first 

 abdominal segment the movable spurs which are elsewhere 

 articulated outside the sacs are wanting, but this is probably 

 to be regarded less as a primitive condition than as a sup- 



* Boll. Soc. Ent. Ital. xviii. (1880), p. 6, and xix. (1887), p. 7. 



