288 SUMMARY OF CUREENT RESEARCHES RELATING TO 



essentially in the continued production of new nuclear material like that 

 already present, and without the periodical recurrence of metamorphosis. 

 The act of division itself is very probably a mere physical incident of 

 the increasing volume of substance. Mitosis on the other hand is very 

 evidently associated with cyclical processes in the nucleus, for alternate 

 departure from and return to certain conditions are characteristic 

 features. The author deals with the hypothesis of "chromosome- 

 individuality," which he regards as very improbable as a universal 

 hypothesis. 



Development of Polypterus.* — J. Graham Kerr gives a short 

 account of some of his observations on the development of Polypterus 

 senegalus from the Niger. The buccal cavity is from the beginning 

 widely open ; the secretory epithelium of the cement organs is endo- 

 dermic in origin, arising as a pair of diverticula from the anterior end of 

 the gut, like gill-pouches ; the lung rudiment is at first median and 

 ventral ; the pancreas arises from three diverticula ; the " liver " is really 

 a hepatopancreas. The author gives a short account of the development 

 of the kidney and the vascular system, and makes some notes on the 

 early skull which has some resemblances to that of Amphibia. The 

 cavity of the dorsal aorta is formed by the fusion of vacuoles in masses 

 of protoplasm derived from the sclerotomes. The endocardium is 

 apparently mesodermic in origin. It is suggested that the blood 

 corpuscles are mesodermic cells set free from their neighbours by the 

 drawing in of cell processes accompanying an epidemic of mitosis. 

 During a prolonged period only one pair of aortic arches is present — 

 those of the external gills (hyoidean). 



Regeneration of the Lens in Amphibian s.f — Hans Spemann 

 makes some new contributions to this interesting subject. In Rana 

 esculenta the lens may develop without any stimulus on the part of the 

 optic vesicle. The primordium of the retina in the medullary plate was 

 excised with a glass needle, yet sections showed on the eyeless side the 

 rudiment of a lens or a well-formed lens with fibres. But in Ranafusca 

 similar experiments had a negative result. Some other very remarkable 

 experiments are recorded. 



Agenesis of the Vermiform Appendix. | — H. T. Marshall and 

 R. T. Edwards describe a case in which there was no appendix visible 

 on external examination of the caecum. Microscopical examination 

 showed only a rudimentary stracture, which extended as a shallow 

 invagination of the mucosa of the cascum from its lumen, ending 

 between the fibres of the circular muscle of the caecum. 



Histogenesis of the Retina. § — A. W. "Weysse and W. S. Burgess 

 have studied the development of the retina in the chick. It consists at 

 first of a syncytium. Most of the nuclei eventually go to form the 

 gangHon-cell layer ; those next the external limiting membrane become 



* Proc. R. Phys. Soc. Edinburgh, xvii. (1907) pp. 73-5. 

 t Zool. Anzeig., xrxi. (1907) pp. 379-86. 



X Philippine Journ. Sci., i. No. 10 (1906) pp. 1061-5 (3 pis.). 

 § Amer. Naturalist, xl. (1906) pp. 611-37 (17 figs.). 



