SECTIONAL TRANSACTIONS.— D. 369 



velocity of fatality, there is no theoretical limit to the toxicity of lead in dilute 

 solutions. 



The velocity of fatality curve, though definite in outline, does not entirely 

 conform to the normal standard for toxic substances ; an interesting problem is 

 suggested with regard to the definition of toxic action in general. 



25. Mr. J. T. Cunningham. — Experiments on Artificial Cryptorchidism, 

 and Ligature of the Vas deferens on Spermatogenesis in Mammals. 



It has long been known that the undescended testis in the condition termed 

 cryptorchidism is sterile. It was suggested by Dr. F. A. E. Crew that the reason of 

 this was the higher temperature in the abdominal cavity than in the scrotum. The 

 same suggestion was made by Mr. Carl R. Moore, of Chicago, who has published 

 evidence in support of it. Mr. Cunningham described an experiment made by himself 

 on a rabbit, showing that in a testis detached from the scrotum and placed in the 

 abdomen the seminal tubules degenerated and the interstitial tissue was relatively 

 greater in amount, while the testis of the side not operated upon remained normal. 



Three other experiments on male rabbits described in the paper confirmed the 

 results of Mr. Carl R. Moore and his American colleagues, showing that ligature of 

 the vas deferens in the abdomen did not cause degeneration of the seminal tubules 

 with apparent increase of interstitial tissue. 



The paper supported the conclusion that the results attributed to ligature of the 

 vas deferens were really caused by some alteration in the normal position of the testes 

 in the scrotum. 



Exhibits. 

 Mr. G. E. DE Beer : — 



1. Models illustrating Chondrocrania (Cartilaginous skulls of embryos). 



2. Preparations showing the Development of the skeleton of the Fowl. 



3. The Histology of the Pituitary body. 



Mr. G. L. Purser. — Calamoichthys (drawings, &c.). 



Dr. Heslop Harrison. — Specimens showing inherited Melanism. 



Mr. Tate Regan, F.R.S. — Fishes from Lake Nyasa. 



Dr. Monica Taylor. — Amoeba, &c. 



The Exhibition included : — 



I. Laboratory cultures of Amoeba prolans, microscopical preparations of the 

 living animal and a series of preparations illustrating its life-history. 



II. Micro-aquaria illustrating the technique of cultivating some animal types 

 useful for biological teaching. 



Amoeba protens, the largest of the free-living amoebae, though widely distributed, 

 is difficult to obtain in large numbers, to time, at all seasons of the year. It is largely 

 employed for all kinds of biological work and for teaching. Flourishing laboratory 

 cultures are, therefore, a desideratum. 



Frequent fission divisions characterise the adult amoeba. True mitosis has not 

 yet been observed in the nuclear divisions. The adult nucleus consists of a centrally 

 placed karyosome connected by an achromatic network with the nuclear membrane, 

 and lying in the nuclear sap. The chromatin occurs in several hundred small blocks 

 lying under the nuclear membrane. A rudimentary form of mitosis occurs in the 

 division of these blocks, which increase in number as the nucleus grows. 



Its fission cj'cle being over, the amoeba proceeds to form encysted young, a 

 phenomenon which can frequently be detected by the pK of the water of the culture. 

 This phenomenon is initiated by the escape of chromatin blocks (c/. chromidia) from 

 the nucleus into the surrounding cytoplasm, where they set up activities in which 

 the nutritive spheres of the mother amceba play an important part, the end-result 

 being the formation of a large number of minute (5[ji diameter) encysted young 

 amoebae. 



The whole of the nucleus of the mother amceba is not used up in the process. The 

 ectoplasm of the mother amceba forms a thin covering round the encysted young. 

 When it disintegrates, these latter fall to the bottom of the aquarium. After a period 

 of time, the young hatch out, and attain maturity in about six months. 



1926 B B 



