THE EVIDENCE OF THE THYROID GLAND 215 



secretion into the blood and lymph, and this latter secretion may be 

 of the most vital importance. Now, the striking fact forces itself 

 prominently forward, that the thyroid gland of the higher vertebrates 

 is the most conspicuous example of the importance of such internal 

 secretion. Here, although ductless, we have a gland which cannot 

 be removed without fatal consequences. Here, in the importance of 

 its internal secretion, we have a reason for the continued existence 

 of this organ ; an organ which remains much the same throughout 

 the Yertebrata down to and including Petromyzon, but, as is seen 

 at transformation, is all that remains of the more elaborate, more 

 extensive organ of Ammoccetes. Surely we may argue that it is 

 this second function which has led to the persistence of the thyroid, 

 and that its original form, without its original function, is seen in 

 Ammoccetes, because that is a larval form, and not a fully-developed 

 animal. As soon as the generative organs of Petromyzon are developed 

 at transformation, all trace of its connection with a genital duct 

 vanishes, and presumably its internal secretory function alone remains. 



Yet, strange to say, a mysterious connection continues to exist 

 between the thyroid gland and the generative organs, even up to 

 the highest vertebrate. That the thyroid gland, situated as it is 

 in the neck, should have any sympathy with sexual functions if it 

 was originally a gland concerned with digestion is, to say the least 

 of it, extremely unlikely, but, on the contrary, likely enough if it 

 originated from a glandular organ in connection with the sexual 

 organs of the palasostracan ancestor of the vertebrate. 



Freund has shown, and shown conclusively, that there is an 

 intimate connection between the condition of the thyroid gland and 

 the state of the sexual organs, not only in human beings, but also 

 in numerous animals, such as dogs, sheep, goats, pigs, and deer. He 

 points out that the swelling of the gland, which occurs in consequence 

 of sexual excitement (a fact mentioned both in folk-lore tales and in 

 poetical literature), and also the swelling at the time of puberty, may 

 both lead to a true goitrous enlargement ; that most of the permanent 

 goitres commence during a menstrual period ; that during pregnancy 

 swelling of the thyroid is almost universal, and may become so ex- 

 treme as to threaten suffocation, or even cause death ; that the period 

 of puberty and the climacteric period are the two maximal periods 

 for the onset of goitre, and that exophthalmic goitre especially is 

 associated with a special disease connected with the uterus. 



