374 SECTIONAL TRANSACTIONS.— D. 



change appears to be accompanied by a change in metabolism. This may be 

 due to external factors, but in higher forms, as in Lymantria or Amphibia, 

 depends mainly on internal factors. It can, however, be affected by external 

 factors even in these forms. Examples are given of alterations of the time 

 of metamorphosis by various factors. It is pointed out that by this means we 

 can study the time-relations of developmental processes. For instance, the fact 

 that Urodele larvae kept at low temperatures reach a greater size before meta- 

 morphosing than do those kept at optimum temperatures indicates that cold 

 decreases the activity of the processes leading to thyroid differentiation more 

 than it does those leading to general growth of the rest of the larval organism. 

 The failure of Perennibranchiates to metamorphose in spite of possessing active 

 thyroids was discussed, and the idea of a balance between thyroid and the 

 metabolism of other tissues of the larva, a balance which may be altered by 

 changes in either member of the pair, was stressed. 



22. Dr. F. A. E. Ceew. — Dsvelopmental Inter sexuality in the 



Domesticated, Mammals. 



Abnormality of the reproductive system taking the form of an intimate 

 mixture of male and female structures is by no means rare in the domesticated 

 mammals. Many cases in the horse, pig, goat, and cattle have been examined 

 and in all the general condition is the same. It is reasonable, therefore, to 

 conclude that the underlying cause is similar. The history of many such cases 

 is that an individual, regarded as a female for the first year or so of its life, 

 assumes certain characters of the male. The condition is best explained on the 

 assumption that such individuals are males in which sex-differentiation has been 

 much delayed. The process of differentiation consists of two stages : in the 

 first, the gonads become differentiated ; in the second, under the direction 

 of the sex-hormone, the remaining structures of the sex-equipment are modelled 

 to one of two plans, the male or the female. If the first stage is delayed, the 

 sex-hormone is not exhibited, and in the absence of any specific control the 

 Wolffian and Miillerian ducts pursue an equal and parallel development under 

 the common stimulus of nutrition ; the urogenital sinus with its genital tubercle 

 becomes a well-grown cleft with a phallus in its ventral commissure. Later, when 

 the gonads become differentiated, only tliose structures which are not too full- 

 grown can respond to the stimulus of the sex-hormone. It is because the 

 undifferentiated full-grown form is more closely mirrored by the immature 

 female that the individual is regarded as a female. 



23. Dr. A. Smith Woodwaed. — Demonstration of a model of the 



Rhodesian Skull. 



24. Miss A. Dixon. — The Periodicity in the Protozoan Fauna of a 



Pond. 



An investigation, by means of weekly collections of pond material, was made 

 in a Manchester pond during thirty-four months. The results show that there 

 is a marked periodicity in the freshwater protozoa, many showing a double 

 rhythm, with the maxima in the autumn and spring months, which is shown by 

 an increase of species, as well as an increase of individuals. Many of the 

 bottom-loving species in the maximum periods spread to the mid and surface 

 layers of the water, where they are found at no other times. There is less 

 evidence of periodicity at the bottom, where many are continuous. Some of the 

 smaller fluctuations in protozoan numbers appear to be due to the changes in the 

 amount of suftshine, which, except for protozoa having chromatophores, has 

 on the whole a depressing influence. The time for least activity in the protozoa 

 fauna is in June, July, and December. 



25. Dr. J. W. MuNRo. — The Natural History of the Large Pine 



Weevil. 



The Large Pine Weevil — an important enemy of young forest plantations. 

 General life-history and relation to the forest. Common control measures used 



