224 SOME NEW BOOKS [September 



by Dr. Sharp last year at Cambridge before the International Zoological 

 Congress. Here he restricts himself to a record of the facts of insect life and 

 structure, and perhaps by the absence of any trace of a phylogenetic tree he 

 silently rebukes the rashness of younger men. Geo. H. Carpenter. 



DR. WILLEY'S RESULTS. 



Zoological Results based on Material from New Britain, New Guinea, 

 Loyalty Islands, and elsewhere. Collected during the years 1895, 

 1896, and 1897. By Arthur Willey, D.Sc. (Loud.), Hon. M.A. 

 (Cantab.) Part III. pp. 207-356, pis. xxiv.-xxxiii. Cambridge Uni- 

 versity Press, 1899. Price 12s. 6d. 



Part III. of Dr. Willey's "Zoological Results " contains articles by Dr. 

 Gadow, Mr. Shipley, and the author. Dr. Gadow gives an interesting account 

 of the variations to be found in the carapace of young chelonians. We 

 must assume that the course of evolution in the chelonian branch of reptiles has 

 been in the direction of a steady reduction in the number of scutes covering the 

 carapace, in accordance with a "widespread evolutionary law" of the "specialised 

 few" replacing the "generalised many." 



The turtlets show a greater percentage of abnormalities in the carapace than 

 the older individuals. " Our Turtlets start with many, with at least 24 dorsal 

 scutes (leaving out the marginals), and then reduce them to 16. In other 

 genera the reduction has advanced to 14, to 13, and individually to 12. This 

 means onward development. The ideal, the goal for the young Caretta, is the 

 possession of a 16-scuted shell. Those which start with 24 perhaps never reach 

 the ideal, but this failure does not seem to hurt them, natural selection remains 

 indifferent. Others start with 22, 21, 20, 19, or 18 scutes, and the latter 

 individuals are rather common in the newly-hatched stage, and all of these seem 

 to reach the goal. . . . These variations from the normal type all lie in the 

 direct line of descent, and the more serious the variation the farther back it 

 points. Moreover, the changes necessary to turn any given variation into 

 another one less abnormal, until ultimately the normal condition is reached, are 

 not erratic, but stand in strict correlation with each other, and proceed strictly 

 on definite lines. I therefore call this kind of atavistic variation ort/wgenetic." 

 This orthogenetic variation in young chelonians appears to be a very striking 

 example of Van Baer's law in its modern application. 



Dr. Willey follows with a valuable contribution to our knowledge of the 

 Enteropneusta, Firstly, he gives a synopsis of the groups under the three 

 families of Ptychoderidae, Spengelidae, and Balanoglossidae, followed by a detailed 

 description of Pti/chodera fiava, P. carnosa n. sp., P. ruficollis n. sp., with 

 Spenc/elia porosa, Willey, and >$'. alba n.sp., with notes upon the West Indian 

 species Pt. biminiensis n.sp., and Pt. jamaicensis n. sp. 



There are many interesting points upon which one could dwell in these 

 descriptions, but space will not permit. Spengelia appears to offer some 

 remarkable features, including the so-called vermiform process of the stomochord 

 (the latter is a useful name suggested by the author for the " notochord " of 

 the Enteropneusta), and the presence of truncal canals. Dr. Willey finishes his 

 paper by a discussion of the " Morphology of the Enteropneusta." He pro- 

 pounds a theory of the origin of gill-slits, based principally ou their relation- 

 ship to the gonads in this group. 



Gill-slits primarily arose as inter-zonal depressions between the zonary, 

 metamerically repeated gonads, functioning for the oxygenation of the gonads. 

 Later they acquired openings into the pharyngeal wall, and were used for the 

 respiration of the individual. 



Further, he comes to important conclusions with regard to the stomochord of 

 Enteropneusta and related organs in Cephalodiscus and Actinotrocha, which 



