Mat 20, 1910] 



SCIENCE 



789 



of both species of Nezara of a quadripartite 

 chromosome, composed of two somewhat un- 

 equal components and having exactly the form 

 of a butterfly with wide-spread wings. This 

 element, always lying in the outer ring and in 

 constant position with respect to the spindle- 

 axis, divides equally into two double elements. 

 Each spermatid-nucleus thus receives six 

 single chromosomes (including one idioehro- 

 mosome) and one double element; though the 

 duality of the latter is often obscured in the 

 later anaphases. This phenomenon may indi- 

 cate that a change in the chromosome-number 

 is in progress, the double element represent- 

 ing either the initial stages in the separation 

 of one of the " autosomes " into two (as ap- 

 pears to have occurred in case of the X-chro- 

 mosome of Syromastes, Fitchia, etc.) or the 

 final stage of a fusion of two into one. 



Edmund B. Wilson 



the structural characteristics and rela- 

 tions of the apodal fishes' 



The characteristics and relations of the 

 Apodals (Apodes) have been involved in much 

 uncertainty even to the present hour. Never- 

 theless, no order appears to be really more 

 trenchantly difEerentiated when a sufficient 

 number of skeletons is at hand. Their chief 

 characteristics of ordinal value may be given 

 as follows: 



Order Apodes 



The order of eels or apodals is composed of 

 fishes with a skull specialized especially by its 

 extension forwards and the coalescence of the 

 ethmoid, vomer (and premaxillaries?) into one 

 piece which projects and is clamped laterally 

 and more or less backwards by the maxillaries, 

 the fusion with the vomer ( ?) or loss of the 

 premaxillaries, the slight development of the 

 palatal and pterygoid systems, the junction 

 of the parietal bones, the presence of a chain 

 of suborbital bones, the single cotyloid condyle 

 for the articulation of the vertebral column, 

 the freedom and reduced development of 

 the shoulder girdle (and in some the com- 

 plete loss), the single eoraco-scapular plate 



' Abstract of a communication to the National 

 Academy of Sciences, April 21, 1910. 



in which are ossified the hypereoracoid and 

 hypocoracoid, the mesoeoracoid being lost, 

 the brain of the ordinary teleost type but with 

 secondary olfactory lobes in front of the prin- 

 cipal ones, the great development of the 

 branehiostegal apparatus, and the development 

 of a pneumatic duct between the air-bladder 

 and alimentary canal, and the loss or abdom- 

 inal position of the ventral fins. The species 

 propagate in the sea and pass through a pe- 

 culiar stage known as the Leptocephalus or 

 Atopichthys form, a ribbon-like translucent 

 condition from which develops a later eel-like 



All the known species have the familiar 

 eel-like form in varying degrees, some being 

 much stouter and others excessively elongated, 

 but the form is not an ordinal character, al- 

 though in this case to a large extent coordi- 

 nated with such characters. The absence of 

 ventrals which gave name to the order 

 (Apodes) is falsified by extinct representa- 

 tives of the family Anguillavidffi, although 

 justified by all the living species. 



Inasmuch as much difference of opinion 

 has prevailed respecting the homologies of the 

 supraoral dentigerous bones, and as silence 

 respecting them might be interpreted as the 

 result of ignorance or undue disregard of 

 others, some explanation seems to be called 

 for here. By many of the old anatomists, the 

 upper lateral dentigerous bones were consid- 

 ered to be palatines, but that view, for the 

 most part, has been long abandoned. Recent 

 high authorities, however, have regarded the 

 bones in question as not homologous for the 

 Mursenids compared with the rest of the 

 Apodals. While the upper bones of the An- 

 guillids and other platyschistous eels have 

 been admitted to be maxillaries, the lateral 

 dentigerous bones of the Muraenids have been 

 homologized with the palatines or pterygoids. 

 In other words, according to one author, the 

 Mursenids have the " maxillaries absent, re- 

 placed by the palatopterygoid, the mouth bor- 

 dered by the latter and the ethmo-vomer," ac- 

 cording to another, by " the toothed ethmo- 

 vomer and pterygoids." Such an interpretation 

 implies that the dentigerous bones, so much 



