470 ZOOLOGY. 



CLASS OF MYZONTS. 



Scott (W. B.). Beitrage zur Entwickelungsgeschichte der Petromyzonten. Morplio- 

 log. Jalirb.,v. 7, pp. 101-172, 5 pi. 



Eiiibryology of the Lamprey. 



An important contribution, in the German language, to our knowl- 

 edge of the development of the Petromyzontids is due to Mr. W. B. 

 Scott, of Princeton, New Jersey. In the laboratory of Professor Gegen- 

 baur, at Heidelberg, he instituted new investigations on the family in 

 question, and has published the result in an elaborate memoir in Gegen- 

 baur's Morphologisches Jahrbuch (v. 7. pp. 101-173, with 5 pi.). We 

 can only notice a few of the fruits of his studies. 



The gastrula is the result of a true invagination, (but it is not central 

 as it is in Amphioxus,) and the overgrowth of the smaller elements. 

 The notochord was found to be of endodermal origin as has been 

 known to be the case in the Leptocardians, Selachians, true Fishes, Uro- 

 dele Amphibians, Lacertilian Eeptiles and Mammals. Eight pairs of 

 branchial clefts are developed, but the foremost speedily disappears, 

 and it is added that there is no evidence of the existence of gill clefts 

 anterior to the first pair of the lamprey in any primitive vertebrate. 

 The embryonic mouth develops into the mouth of the adult, while in 

 the higher vertebrates, save the Teleost fishes, the medullary tube 

 arises from the growth together of two folds in the lamprey. The folds 

 are appressed, and " the medullary tube forms an inwardly projecting 

 knob, which, when it is separated off from the ectoderm, is at first a 

 solid tube, and only becomes hollow by the outgrowth of its cells." 

 The sensory organ first developed is the auditory, and this appears 

 just in front of the primitive vertebra (and not, as in the Selachians, at 

 some distance from it). The brain is notable in that for some time 

 " there is no tendency to folding ; when it does occur it appears to be 

 due to the sudden increase in growth of the median portion." The ru- 

 dimentary olfactory organ was found to be primitively single (and not 

 double, as described by Calberla). 



Some of the observations and inferences of Dr. Scott, especially those 

 on the germinal layer, have been since controverted by J. P. ISTuel, 

 (Archives de Biologic, t. 21, pp. 403-454, with 2 pi.), but the memoir 

 noticed is one of sterling merit and noteworthy as the production of an 

 American naturalist. 



CLASS OF SELACHIANS. 



Balfour (F. M,). On the Development of the Skeleton of the Paired Fina of Elasmo- 

 branchii, considered in Relation to its Bearings on the Nature of the Limbs of the 

 Vertebrata. Proc. Zool. Soc. London, 1881, pp. 656-€71, 2 pi. 



Benda (Carl.). Die Dentinbildung in den Hautzahnen der Selachier. Arch. f. 

 mikroskop. Anat, v. 20, pp. 246-270, 1 pi. 



Bolau (H.). tJber die Paarung und Fortpflanzung der Scyllium-Arten. Zeitschr. 

 Wiss. Zool., V. 35, p. 321-325. 



