Januabt 7, 1916] 



SCIENCE 



35 



tion is a violent poison because of its arsenic 

 content and althongli tobacco leaves contain 

 nicotine which when in solution is an effective 

 parasiticide, yet these agents in their dry state 

 do not destroy mites. 



. Duplicate tests were run with naphthalene 

 or powdered moth balls which on account of 

 its volatile substances emitted, killed all mites 

 in the tests in 45 minutes. 



Insect powder containing gasoline and crude 

 carbolic acid, on account of the volatile sub- 

 stances given off, killed all mites in one 

 minute. 



In duplicate tests, solutions sufficiently con- 

 centrated kiUed in the following lengths of 

 time: Crude carbolic acid, 20 seconds. Five 

 per cent, carbolic acid, one minute. One per 

 cent, naphthalene in kerosene, 30 seconds. 

 One per cent, kreso dip ten minutes and two 

 per cent, four minutes. Ten per cent, formal- 

 dehyde ten minutes. 



Conclusions 

 In order that parasiticides be effective in 

 the destruction of the mites they must either 

 be in solution or be capable of giving off vola- 

 tile substances which in themselves are de- 

 structive. B. F. Kaupp 

 North Carolina Experiment Station, 

 West Raleigh 



THE GROWTH OF BONE IN CRETACEOUS TIMES 



Paleontologists have, for many years, been 

 acquainted with the curious conical portions 

 of young plesiosaurian propodials and, also, 

 they have observed definite openings on the 

 edges of many of the flattened limb bones. 

 One of these openings has, in some cases, been 

 observed to lead into a canal, which, in turn, 

 passes into a cavity, remarkably like the medul- 

 lary canal of mammalian long bones. There 

 has never been an adequate explanation for 

 these curious conditions. 



It has been generally assumed that the un- 

 usual characters mentioned above have been 

 confined to the propodium (humerus or 

 femur) but, recently, in studying the osteology 

 of an immature plesiosaur from the Cretace- 

 ous, the writer noted all of these characters in 

 a phalangeal bone. Further study of this prob- 



lem will doubtless result in the discovery of 

 these characteristics in all the long bones of 

 the skeleton, especially in young and immature 

 animals. 



Andrews, Williston, Lydekker, Kiprijanoff 

 and the writer have remarked on the unusual 

 characters of this ancient group of aquatic 

 reptiles and an attempted explanation^ has 

 been given of the curious conical ends of young 

 propodials which formerly were regarded as 



In regard to the openings, canal and cavity, 

 the writer believes an adequate explanation of 

 this condition is to be found in the develop- 

 mental history of the mammalian long bones. 

 Szymonowicz^ has figured in a developing long 

 bone of a mammal an opening which he terms 

 " periosteal bud," similar in all respects to the 

 opening in the edge of plesiosaurian limb 

 bones. In both eases a canal leads from the 

 foramen into the medullary cavity. 



Jackson^ has given a careful description and 

 figure of a similar condition in the tibia of a 

 three-day cat. Through this opening the blood 

 vessels supplying the medullary cavity, the 

 osteoblasts and marrow-forming elements 

 migrate from the periphery into the medullary 

 cavity. 



Bidder* has further studied the conditions 

 of bone formation and his contribution has 

 suggested an explanation for certaiu curious 

 features in the propodials of the plesiosaurs. 

 The question arises as to whether it is legiti- 

 mate to interpret developmental factors in the 

 ancient reptiles from what occurs in modern 

 mammals. That question is not yet settled, 

 but assuming that an analogy may be safely 

 drawn between developmental features in the 



1 Moodie, Eoy L., "Eeptilian Epiphyses," 

 Amer. Jour. Anat., Vol. 7, No. 4, pp. 443-467, 

 Figs. 1-24, 1908. 



2 Szymonowicz, L., "A Text-book of Histology 

 and Mieroscopie Anatomy of the Human Body, ' ' 

 trans, by MacCaUum, 1902, p. 270, Plate XXIX. 



3 Jackson, C. M., ArcMv fiir Anat. u. Physiol., 

 Anat. AbtJi., Jdhrg., 1904, p. 33, Taf. VII., 

 Fig. 1. 



4 Bidder, Alfred, 1906, " Osteobiologie, " ArcMv 

 f. mikros. Anat., Bd. 68, pp. 137-210, Taf. X-XFV. 



