PATHOLOGICAL STATES IN EVOLUTION. 249 



hernia seems to have occurred ahnost universally and to have 

 established itself as noroially physiological. The tunica vaginalis 

 propria of the testis is actually part of the original peritoneal sac, 

 as can be seen in the embryo. During foetal life it is separated 

 from the parent tissue. In whatever sense we now call such a 

 change physiological it seems impossible to regard it as originally 

 anything but pathological. Is it too startling to declare that it 

 is an evolutionaiy sloughed tissue such as is often seen in 

 strangulated hernias ? I certainly do not know how we can 

 describe the scrotum as anything else than the coverings of an 

 evolutionaiy hernial sac which is not only of no advantage but a 

 positive danger to most male animals. In some, the pigs for 

 instance, the testicles do not descend into an external pouch but 

 are supported and protected by the normal skin tissues, not by a 

 thinned and delicate integument of later development like the 

 scrotum, a tissue still scantily supplied with the non-striated 

 muscular fibres which might have reinforced it and are perhaps" 

 now developing slowly. When we consider the i^arity of mus- 

 cular fibres in human skin tissues in compai-ison with those of 

 animals, their greater frequency in the scrotum and perinseum 

 suggests that they are a reaction product. They act in the 

 dartos, or deeper layers of the scrotal dermis, at right angles to 

 the rugfe and are something of a support. The pink colour of 

 this structure is due to the presence of these muscular fibres. 

 They are not connected in any way with the cremaster muscle 

 and therefore not afiected by the cremasteric I'eflex. In no sense 

 can the descent of the testes be called a.dvanta.geous. It causes 

 a weak spot, recognized as such by men and animals. The 

 Japanese wrestlers are trained from youth to return the testes 

 into the inguinal -canals. If the translation of the testis from 

 a safe place to an exposed one has had any good results they 

 have been indirect and only discoverable, though not yet 

 discovered, over long periods during which the change must 

 have been disastrous to many. To argue that they were advan- 

 tageous to begin with is to destroy the authority of reason. 



It may seem an undue extension 'of the view that pathology 

 has played an immense part in evolution if it is suggested that 

 it was upoii pathological conditions that the very existence of 

 the Metazoa depended. There can be no doubt that they origi- 

 nated from some protozoon by a failure of normal physiological 

 fission. We see here how theories of disease may be modified 

 according to the point of view ta,ken From that, shall I say, of 

 a protozoan Hippocrates or Hunter nothing can be more obvious 

 than that a failure of mitosis would be a calamity, the birth of a 

 monster, of Siamese twins, among the normally constituted uni- 

 cellular organisms. It is still in the processes of reproduction 

 that we find the strongest evidence of the part played by disease. 



When considering such problems in this light it seems some- 

 what difficult to account for the satisfaction of many with the 

 theory of small cumulative advantageous variations. What ground 



