1903.] The Acquirement of Secondary Sexual Characters. 51 



frontal behind the orbit lies almost at a right angle with the inter- 

 orbital portion of the bone, the horn-cores arising from the upper or 

 horizontal area. 



Although the skull generally is thicker in either case than in the 

 wether, this alone does not account for the difference in external 

 form • the cranial cavity presents a corresponding extension in the 

 frontal region. 



In the configuration of its skull, as in the absence of horns, the 

 castrated animal precisely resembles the hornless ewe of the breed. 



We have studied the effects of the same procedures upon sheep of a 

 well-known pedigree Southdown herd. The result in such animals is 

 less striking than in the Herdwick, partly because each sex is hornless, 

 and partly because amongst Southdowns individual variations in the 

 form of the head are not uncommon : thus, whilst the head of the 

 wether usually offers a marked contrast to that of the ram, in certain 

 cases the characters of the two so nearly approximate that even an 

 expert may find it difficult to distinguish between them, the ram under 

 such circumstances being commonly called " wether-headed." 



In the Southdown there is not (as in -the Herdwick) any marked 

 difference produced by castration in the form of the forehead, the angle 

 between the pre- and post-orbital portions of the frontal bone being 

 equally obtuse in the vasotomised sheep and the wether, and this, for 

 the reason that both are equally destitute of horns. 



That the occlusion of the vas had been complete in all the cases 

 observed, was proved by a careful dissection of the testicles after the 

 animals were killed. 



Seeing that the full development of male characters proceeds in spite 

 of double vasotomy, it becomes interesting to inquire into the condition 

 of the testicles and into the sexual physiology of the animals themselves. 



To take the latter first. A Southdown, the subject of double 

 vasotomy when a lamb, and kept apart until full grown from any 

 female, was turned loose with a couple of maiden ewes ; he at once 

 copulated, erection and intromission being complete. The two ewes 

 were not again admitted to the flock, but were kept apart, with the 

 result that neither afterwards proved to be in lamb. This animal was 

 killed 18 months after the vasotomy. The testicles had, from the first, 

 grown symmetrically, and had reached the normal size; dissection 

 revealed a complete interruption of each vas close above the gland. 



In certain cases one of the testicles underwent a marked diminution, 

 i.e., it not merely failed to grow but rapidly wasted. In the other 

 cases both organs attained the full dimensions. These differences are 

 to be ascribed to differences in the condition of the blood-supply ; when 

 the vas is cleanly isolated and divided after ligation without the 

 inclusion of vessels, or without the subsequent occurrence of thrombosis, 

 no atrophy of the gland ensues. When atrophy of one testicle arises, 



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