Mabch 19, 1915] 



SCIENCE 



437 



groove. This is continued forward between the 

 skin and the pelvic arch where it enlaiges to 

 form a sac, which in its turn is extended forward 

 as a tube between the skin and the belly wall. 

 Each tube ends blindly near the median line, in 

 some extending nearly to the pectoral girdle. The 

 function of this organ is entirely unknown. 



These structures were described from Sypo- 

 prion irevirostris and signattbs, and from the 

 tiger shark, Galeocerdo tigrinus captured at Key 

 West and at Tortugas, Florida. The longest gland 

 (one foot, 7f inches) was found in a 4 foot, 10 

 inch specimen of S. signattis. 



The scanty literature of this organ from its 

 discovery by Andrew Smith in 1849 was briefly 

 sketched. The full data will be given later in an 

 article in "Papers from the Tortugas Labora- 

 tory, ' ' published by the Carnegie Institution of 



Fre-Otio Somites in Cyclostomes : H. V. Neal. 



(With lantern.) 



Concerning no other criterion of the metamer- 

 ism of the vertebrate head do observations so 

 fully agree as with regard to the mesodermic di- 

 visions discovered by Van Wi-jhe ('82) in Selach- 

 ian embryos. His discovery has been confirmed by 

 Miss Piatt ('91), Hoffman ('94), Neal ('96), 

 Sewertzoff ('98), Braus ('99) and Johnston 

 ( '09). Moreover, SewertzofE showed that the more 

 numerous "microccelie" divisions described by 

 Dohrn ('90) and Killian ('91) in Torpedo em- 

 bryos secondarily unite to form the somites of 

 Van Wijhe. Furthermore, a mesodermic segmen- 

 tation which may be compared with that of Elas- 

 mobranchs has been discovered by Miss Piatt 

 ('97) in Amphibia and by KoltzofE ('02) in 

 Cyclostomes. 



The mesodermic segmentation discovered by 

 Koltzoff ('01) in Petromygon embryos is espe- 

 cially significant and important, since in this ani- 

 mal according to KoltzofE the segmentation of the 

 head mesoderm is complete as in Amphioxus and 

 the somites develop as dorso-lateral diverticula of 

 the endoderm. Thus Petromyzon is in this re- 

 spect as in others intermediate between Acrania 

 and Gnathostomata. Koltzoff finds that the three 

 anteriormost somites give rise to the eye muscles 

 as they do in the Elasmobranchs. 



The importance of the evidence as bearing on 

 the past history of the vertebrate head has led me 

 to examine sections of Petromyzon embryos in the 

 hope of confirming KoltzofE 's results. In at least 

 two series of eight-day Petromyson planeri em- 



bryos the evidence presented seems to bear out 

 Koltzoff 's contention that the pre-otic segmenta- 

 tion of the mesoderm is comparable with that of 

 Elasmobranch embryos. The anterior head meso- 

 derm is completely segmented as Koltzoff has as- 

 serted. No homologue of Miss Piatt 's ' ' anterior ' ' 

 somites, however, is present in the Cyelostome. 



The Ahsence of Male Beproduetive Organs in Tre- 

 matodes: Feanklin D. Barker. (Lantern 

 slides and demonstrations.) 



Does Amphioxus Eat with His Left Ear?: H. V. 



Neal. (With lantern.) 



It was Van Wijhe ('93) who first suggested the 

 homology of the larval mouth of Amphioxus with 

 the left spiracle of Selachians and asserted that 

 "Amphioxus can not hear; he eats with his left 

 ear and consequently has lost his mouth." The 

 homologue of the craniote mouth in Amphioxus is, 

 according to Van Wijhe, the pre-oral pit. 



The present paper raises the problem : Are we to 

 accept the homology of the mouth of Amphioxus 

 with the spiracular cleft of Craniotes? 



The homology suggested by Van Wijhe is based 

 on the following grounds: 



1. The mouth of Amphioxus is an organ of the 

 left side as evidenced by its development, its left- 

 sided innervation and its topographic relations to 

 the club-shaped gland, which Van Wijhe regards 

 as the antimerio gill-pouch. 



2. The relations of the larval mouth of Amphi- 

 oxus to the second mesodermic cavity and to the 

 splanchnic muscles derived from it are similar to 

 those of the left spiracle of Craniotes to the sec- 

 ond mesodermic head-cavity. 



Van Wijhe 's homology may not be accepted on 

 the following grounds: 



1. Since all median openings of Amphioxus are 

 asymmetrically displaced, the left-sided position of 

 the mouth is not significant. 



2. The left-sided innervation is likewise inde- 

 cisive. If the homology suggested by Van Wijhe 

 were the correct one, the velum should be inner- 

 vated by the left nerve of the third pair. It is 

 actually innervated by the left nerves of the 4-7 

 pairs. Primary nerve relations are obviously dis- 

 turbed and inferences from innervation precari- 

 ous. 



3. The club-shaped gland and its duct represents 

 a pair of gill-pouches and not a gill-pouch of the 

 right side only, as Van Wijhe 's homology would 

 require. The club-shaped gland represents the sec- 

 ond pair of gill-ponches and the endostyle anlage 

 the first pair of gill -pouches of Amphioxus. 



