204 Mr. G. A. Boulenger on some Jurassic and 



liaving ceased to develop at an early stage, and being re- 

 modelled after the fashion of the dipterous larvae which we 

 have been discussing, might have acquired the power of 

 psedogenetic reproduction. I readily admit that our hypo- 

 theses are somewhat many in number ; but there is not a 

 single one among them which has not been actually observed 

 in the Arthropod phylum itself, and more frequently in combi- 

 nations. Whether the leg-stumps of the Tardigrades have 

 arisen by degeneration from Arthropod appendages of their 

 ancestors, or whether they may be new formations like the 

 pro-legs and claspers of the caterpillars, is a question which 

 is difficult to decide. Its solution, however, be it as it may, 

 needs to alter nothing in the whole conception. 



If we once more briefly sum up the points of agreement 

 between the Tardigrades and greatly modified Tracheate 

 larvEe, somewhat of the type of the maggots of Cecidomyia^ 

 we find: — absence of a head, chitinous stylets in the oesopha- 

 geal tube, absence of any ciliated epithelium and of a dermal 

 muscle-sheath, musculature broken up into isolated cords, 

 supra-cesophageal ganglion and ventral ganglion-chain, 

 simple structure of the sexual organs, and, lastly, Malpighian 

 vessels. The differences depend upon further advanced 

 degeneration of the Tardigrades, and include : — small number 

 of the ganglia (disappearance of the parts of the suboesophageal 

 ganglion), smooth musculature, absence of trachese and circu- 

 latory organs, and the probable reduction of the one germ- 

 gland. As new formations we may perhaps regard the 

 efferent duct of the sexual organs and^ at any rate, the leg- 

 stumps, if these are not an ancestral character. 



Embryology as yet affords us no explanation ; besides the 

 development need no longer be of the typical Arthropod type, 

 but may have secondarily undergone great modifications. 



XXX. — On some neicly-descrihed Jurassic and Cretaceous 

 Lizards and lihynciioctphalians. By G. A. BoULENGER. 



In a paper published two years ago (2), whilst dealing with 

 a few points in the osteology of Heloderma and the systematic 

 position of that genus of lizards, I ventured to express some 

 views on the probable phylogeny of the order Squamata, 

 which comprises the existing group of true lizards, chame- 

 leons, and snakes. I pointed out that the Cretaceous lizard 

 Hydrosaurus lesinensis^ regarded by some authors as a member 



