TRANSACTIONS OP SECTION D. 405 



at that time of the year when sexually mature. From this and from what I 

 have to say presently in the case of the blackbird's vernal-moult at the adolescent 

 stage of growth, it is quite evident that it is an unsafe procedure to determine 

 the maturity of a bird by its plumage-markings, and here we may in many cases 

 include colour-changes in the iris and beak and other secondary sexual char- 

 acters when present. 3 The testes at the same time demand anatomical inves- 

 tigation with and without the aid of the microscope. As I have received 

 several blackbirds during the spring of this year, whilst securing the skins for 

 research in other directions, I thought it advisable to take the opportunity of 

 examining the testes with a view of throwing light on the question at issue. 

 Avoiding details in regard to plumage-changes, it may be here noted that, as a 

 rule, there is no difficulty in distinguishing the male blackbird in its first spring- 

 plumage (i.e., when about twelve months old) from the adult of the correspond- 

 ing time of year. For the former is usually very dark brownish-black, with a 

 blackish beak; the latter jet-black, with a deep-yellow beak. But (as in a 

 specimen now before me) the yellow coloration of the beak may appear during 

 the first year coupled with plumage so nearly approaching jet-black that on 

 general inspection the bird in such dress might pass as being fully matured. The 

 yellow beak is usually looked upon as the last sign of maturity ; ' even after 

 assuming the adult plumage, young males of the year have blackish beaks until 

 their second year.' 4 It may be seen from this passage just quoted that here 

 the term 'adult plumage' has been adopted for what seems to me to express the 

 adolescent plumage, which, according to the varying degree of blackness, may 

 approach more or less, or even be practically indistinguishable from, the true 

 adult garb. Again, I have examined an adolescent blackbird obtained in 

 March possessing a yellow beak, but whose blackish-brown under-plumage 

 showed rufous edgings, often present in the plumage of the first winter. 

 Examination of the testes of the above-mentioned birds at once throws light on 

 the question regarding the adult character of the beak. The development of yellow 

 pigment was a matter of precocity, which development outstripped in time the 

 assumption of the true adult plumage, which would not follow till the next year. 

 For the testes showed distinct signs of immaturity. Examined microscopically 

 their greatest length did not exceed 5 mm., their greatest breadth 2-6 mm. On 

 the contrary, in the case of mature birds these organs averaged during the first 

 week of March 1/8 cm. long and 1 cm. broad. Histological examination re- 

 vealed a striking difference. In the adolescent birds the tubules were at least 

 fifty times smaller than were those of the adult. Moreover, in the former there 

 was no sign of spermatogenesis taking place in the tubules, while in the latter 

 countless swarms of ripe sperm-cells occupied the entire microscopic field in one 

 great tubule; one-sixth objective being used in the examination in each case. 

 Hence, in regard to these adolescent birds (examined all about the same time, 

 viz., first two weeks in March), I have no hesitation in expressing an opinion 

 that they would not have reached maturity until the next spring, despite the 

 fact that in one specimen the plumage was nearly fully black and the beak yel- 

 low, and in another specimen with blackish-brown plumage, the beak had 

 turned yellow, bearing in mind that not until the real adult plumage is 

 assumed in the second autumn does the beak usually begin to gain its charac- 

 teristic shade. 



2. A Case of a remarkable Egg of Falco tinnunculus laid under remarkable 

 circumstances. By C. J. Patten, M.A., M.D., Sc.D. 



On Sunday, June 11 last, my tame kestrel, which I have had for eight years, 

 appeared to be in a remarkably lively mood. When let out of her wire 

 enclosure she indulged in her usual trick of pouncing on my shoe and biting at 



3 An interesting experiment illustrating the fact that the close correlation 

 between the assumption of nuptial plumage and sexual maturity may be broken 

 down, is seen when a few of [the first brown feathers of an immature blackbird 

 (male) are pulled out, which are replaced by black, i.e., nuptialoid feathers. 



4 Vide Saunders, Man. Brit. Birds, second edit., 1899, p. 14. 



