«1G 



MU. J, G, H. FREW ON THE LARVAL 



largely to the thin intersegmental membrane, is capable of ii 

 slight degree of protrusion to form a ventral pseiidopocl. 



Iceland the seventh abdominal segment there appears to be one 

 lai'ge segment bearing the longitudinal slit-like anus in its mid- 

 ventral region, and a very small postero-dorsal segment, con- 

 sisting mainly of the two stigmatic papillae and capable of piirtial 

 withdrawal into the apparent segment in front of it. This, how- 

 ever, is not the true nature of this region. A study of the 

 musculature shows that the large segment consists of two seg- 

 ments, abdominal segments 8 and 9, and the small posterior 

 stiguiata-bearing region is almost certainly to be regarded mei-el}'' 

 as a specialized region of segment 9. Some indication of the com- 

 posite nature of the large segment is available without a study 

 of the musculature. In front of the slit-like anus is a transverse 

 row of about 17 sharp, posteriorly-directed, chitinous teeth, and 

 behind it is a small patch of about seven similar teeth pointing 

 forwards. It seems probable that the anterior row represents 

 the posterior band of teeth of segment 8, and the ]>osterior 

 patch the anterior band of segment 9, the anus lying therefore 

 between the two segments. The anus is not bounded by hiteral 

 :swelling.s. 



Cephalo-Pharyngeal Skeleton. 



The form of this is sufficient!}' shown in text-fig. 21, and only 

 two points require special mention, the ventral wall of the jjharynx 



Text- figure 21. 



B. conibitiata. Liiteral view of coplialo-pliiiryngeal sclcrites. 



iind the median ventral piece. The ventral Wiill of the pharynx in 

 the region of the pharyngeal sclerito has distinctly tlie :i|)pearance 

 of being longitudinally ribbed when seen in surface view. As I 

 have not examined sections of the larva, 1 can give no indication 

 of the true nature of these ribs. The median ventral sclerite is 

 a somewhat shield-shaped chitinous plate with its lateral margins 

 bent strongly upwards. Its anterior margin shows a central 

 curved emargination bounded on each side by a rather prominent 

 process from which a cord, apparently of a tendinous nature, goes 

 forward to the ventral process of the corresponding mandible. 

 Posteriorly the plate becomes less heavily chitinized and appears 



