726 J. F. GUDERNATSCH 



suspended in the connective tissue. These muscle fibres are found 

 especially below the aorta, where they approach the follicles and 

 at times surround them. This is accomplished by the fibrillae of a 

 bundle loosening up a little, then enclosing a row of follicles and 

 finally uniting again." 



Regarding the number, size and form of the follicles, all varia- 

 tions exist which have been demonstrated by comparative inves- 

 tigations in the other classes of vertebrates. The size of the fol- 

 licles is, in general, in reverse proportion to their number. The 

 size, however, is not of great importance, since the chief factor 

 in the activity of the gland is the epithelial surface; this will be 

 the larger, the greater the number of small follicles contained in a 

 given region. Biometric calculations would be interesting in this 

 direction as experiments have shown that the functional value 

 of the thyreoid gland varies with the individual. Glands are 

 found in which the size of the follicles is uniform ; in such cases the 

 follicles are usually large. As a rule, however, the follicles are of 

 various sizes as would be expected in view of the process of forma- 

 tion of new follicles. In many cases I have observed that a few 

 (three or four) follicles are unusually large. 



The follicles lying in the central parts are generally larger than 

 those towards the periphery. This seems quite natural in view of 

 the mode of extension of the gland. In only one case, Sarda, do 

 the central portions consist of nests of numerous small follicles 

 while larger follicles lie peripherally (text fig. 12). This con- 

 dition resembles somewhat that in birds (Baber), and mammals 

 (Anderson, Forsyth) and if it be due to the fact that in Sarda the 

 gland is almost as compact (of course without a capsule) as in the 

 higher vertebrates (with capsule) then we must suppose that in 

 such a case new follicles are formed in the centre and are pressed 

 out towards the periphery, while in the breaking up of the gland 

 minute parts are continually carried towards the periphery and 

 there form new follicles. In the first case the peripheral follicles 

 would be the oldest and in the second the youngest ones. 



* Streiff finds muscles between the glandular tissue in the thyreoid of the cat, 

 Zielinska in a young dog, Wolffler in a child (cit. from L. Miiller), L. Midler in an 

 adult woman. The muscle must have migrated into the gland during the first half 

 of the embryonic period, before the capsule was formed. 



