446 NATURAL SCIENCE. Dec, 



body, Dr. Wheeler brings forward evidence to support the accepted 

 view that they are utilised in connection with the reproductive opening. 



Dr. Wheeler's observations upon the origin of the germ-cells 

 confirm, on the whole, the results of Dr. Heymons with PliyUodvomia^ 

 except that doubt is thrown upon their very early differentiation as 

 described by the latter observer. They have now been noticed in all 

 but two of the abdominal segments of embryo insects, recalling very 

 strongly the condition in worms. Dr. Wheeler's researches on the 

 origin of the genital ducts confirm the view that they are modified 

 nephridia. A peculiar mass of cells beneath the oesophagus, 

 developed from the mesoderm of the trito-cerebral somite, is thought 

 by Dr. Wheeler to be a vestigial nephridium, and, accepting the 

 homology of this segment with the antennal segment of the Decapod 

 Crustacea, to represent the green gland of a crayfish. This homology 

 of the segments will bring the antennae of insects into line with the 

 crustacean antennule, and make the mandibles in Crustacea, 

 Arachnida, and Insecta correspond. Dr. Patten, however, insists (4) 

 that no segments have been suppressed in either insects or arachnids, 

 and that the antenna? of the former correspond with the chelicerse of 

 the latter ; but it seems impossible that all the recent describers of 

 vestigial appendages can be mistaken. 



With these contributions to the embryology of insects, it is well 

 to record some recent memoirs upon their development after hatching. 

 Professor Miall (7) has discovered the larva and pupa of a genus of 

 Crane-fly (Dicranota) whose metamorphosis had been previously 

 unknown. The grubs of the " Daddy-long-legs " (Tipula), belonging 

 to the same family, are only too well-known as the "leather-jackets," 

 which often devastate the roots of corn and grass crops. The larva 

 of Dicranota, however, is a flesh-feeder; it lives in gravel and mud at 

 the bottom of streams, and preys upon the well-known red worm, 

 Tubifex. The head of the larva is small, and can be retracted within 

 the thorax. The third to seventh abdominal segments bear pairs of 

 fleshy legs with circles of hooks at the end, recalling the claspers of 

 moth-caterpillars ; the ninth (hindmost) segment carries three pairs 

 of appendages, of which the posterior are long, and contain tracheae. 

 When the head is retracted, the brain, with the subcesophageal and 

 prothoracic ganglia, is found in the mesothoracic segment. The 

 alimentary canal shows adaptation to the carnivorous habit, being 

 straight, and wanting the diverticula found in the grubs of Tipula. 

 As in tipulid larvae generally, there is but one pair of spiracles, 

 situated on the back of the hindmost segment, which is also provided 

 with tracheal gills, so that the grub can breathe by thrusting its tail 

 either into air or water. A well-developed tracheal system provides 

 for the storage of oxygen. The male generative organs develop very 

 early, and ripe spermatozoa were observed in a larva not full-grown. 



The pupa lives in damp earth, and breathes through a pair of 

 y NAT. Sci., vol. i., pp. 54, 55. 



