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



liaviiif; coasccl to develop at an early stage, anil being re- 

 modelled after the fashion of tlie dipterous larva? whicli we 

 have been discussing, might have acquired the power of 

 pfedogenetic 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-stum])S of the Tardigradcs 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 simi up the points of agreement 

 between the Tardigrades and greatly moditied Tracheate 

 larvai, 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-oeso])hageal ganglion and ventral ganglion-chain, 

 sin)plc 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 subocsophageal 

 ganglion), smooth musculature, absence of trachea 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 

 develo] ment need no longer be of the typical Arthropod type, 

 but may have secondarily undergone great modifications. 



XXX. — On some neuly- described Jurassic and Cretaceous 

 Lizards and lihynchocijjhalians. By G. A. BOULENGER. 



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

 a few points in the osteology of Ueloderma and the systematic 

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

 views on the probable phylogcny of the order 8quamata, 

 which comprises the existing group of true lizards, cliame- 

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

 llydrosaurus lesincnsisy regarded by some authors as a member 



