August 29, 1902.] 



SCIENCE. 



351 



The Axial Skeleton of the Enteropneusta, 

 Considered from a Functional Point of 

 Vieiv: William Emerson Ritter, Uni- 

 versity of California. (Will appear in 

 full in 'Scientific Results, Harrinian 

 Alaska Expedition.') 

 (1) The notochord is not restricted to the 

 pouch-like organ present in the adults of all 

 species and hitherto regarded as constitu- 

 ting the entire organ, but in reality extends 

 back to the posterior end of the collar (fully 

 developed in the adult of the Harrimaniidaa 

 and rudimentary in other species). The 

 collar notochord is mainly in the form of a 

 broad, deep trough on the dorsal side of the 

 esophagus, though histologically and func- 

 tionally portions of the esophageal wall 

 adjacent to the trough must be reckoned 

 as belonging to the notochord. (2) The com- 

 bined notochord and chondroid skeletal 

 elements constitute a structural unit, this 

 unit being a true axial skeleton. (3) This 

 axial skeleton has a twofold function; (a) 

 to serve as a firm rod for giving rigidity and 

 strength to the peduncle of the animal, and 

 to support, at its anterior end, the heart and 

 glomerulus which are situated in the base of 

 the proboscis; (6) to serve as the origin of 

 the great radio-longitudinal muscles of the 

 collar. (4) The important muscles above 

 mentioned are attached to the sides of the 

 axial skeleton along its entire length from 

 the mid-peduncle to near the posterior end 

 of the collar. They have an extensive inser- 

 tion into the connective tissue of the collar, 

 the septum between the collar and abdom- 

 inal ccelom, and the collar ectoderm. These 

 muscles are practically the only ones in the 

 collar by which the boring and locomotor 

 movements of the animal are effected 

 there being in this region no body-wall 

 muscles at all in some of the species. They 

 are consequently true skeletal muscles 

 acting on an internal skeleton, and hence 

 having no counterpart in any invertebrate, 

 but are comparable with the axial 



skeletal muscidature of vertebrates. The 

 functional significance of the axial skeleton 

 as above defined has not been recognized 

 heretofore, probably on account of the 

 rudimentary condition of its esophageal 

 portion in most species. In particular, its 

 relation to the skeletal musciilature has 

 escaped adequate recognition. In the facts 

 here briefly set forth we have evidence as 

 strong as that furnished by the branchial 

 apparatus in favor of the chordate affinities 

 of the enteropneusta. 



Evolution and Distribution of the Masto- 

 dons and Elephants in North America: 

 Henry Fairfield Osborn, Columbia 

 University. (Will appear in full in 

 American Naturalist.) 



Ch. Wardell Stiles, 



Secretary. 



SCIENTIFIC BOOKS. 

 The Elements of Insect Anatomy, an outline 

 for the use of students in entomological 

 laboratories. By John Henry Comstock 

 and Vernon L. Kellogg. Third edition, re- 

 vised. Ithaca, N. T., Comstock Publishing 

 Co. 1901. 



Teachers of entomology will certainly wel- 

 come this revised edition of an excellent labo- 

 ratory guide. In their selection of easily ac- 

 cessible types the authors have had in mind 

 the convenience of instructors and classes 

 throughout the country. The outlines are 

 carefully constructed with a view to insuring 

 accuracy of observation and include, perhaps, 

 as much material as can be worked over dur- 

 ing the time usually allotted to the subject in 

 our colleges and universities. The work suf- 

 fers somewhat from lack of symmetry. Thus 

 before introducing the student to the maze of 

 sclerites and other anatomical details, with 

 which the outlines begin, it would have been 

 desirable to insert a chapter on general mor- 

 phology for the purpose of elucidating the 

 important principles of metamerism, cephali- 

 zation, etc. This could have been accom- 

 plished by constructing a number of brief 

 comparative outlines of several insects repre- 



