ANIMAL ANOMALIES . 663 



It is suggested that such individuals have developed from a single 

 zygote which underwent an abnormal cleavage. Examples of these 

 conditions are shown as they occur in cats. Similar fusions occur 

 in human beings as is illustrated in the accompanying diagrams. 



There are also cases of unequal conjoined twins in which a much 

 smaller and less developed individual is fused to the abdomen, head, 

 palate, or sacrum of an otherwise normal individual. Such an indi- 

 vidual is referred to as a parasite on its larger mate. 



Hermaphroditism 



There are abnormal cases of sexual development in vertebrates 

 including man, in which the organs of both sexes are combined in 

 one individual. In true cases there are present both ovaries and 

 testes in the one individual, but no cases are known in which both 

 have functional capacity. The external organs are partly male and 

 partly female, and the secondary sexual characteristics, such as 

 voice, mammae, stature, and beard, may be of a mixed nature. 

 Hermaphroditism is the normal condition in the coelenterates, flat- 

 worms, annelid worms, and molluscs. Here both sets of organs are 

 capable of function. Birds and mammals are rarely subject to this 

 condition. 



A condition spoken of as false herma'plirodiUsm involves the pres- 

 ence of gonads of one sex but the secondary sexual characteristics 

 and external genitalia of the other. In masculine hermaphroditism 

 testes are present but not usually descended into the scrotum, while 

 the external genitalia and secondary characteristics are those of 

 the female. In feminine hermaphroditism ovaries are present, even 

 descended into a scrotum in rare cases, but the clitoris is enlarged 

 and labiae are fused to resemble the penis of the male. In some 

 instances the lips of the slitlike urinogenital aperture on the under 

 side of the penis fail to fuse. 



There is a very close homology in the organs of the two sexes. 

 The external genitalia are indifferent or sexless until the end of the 

 seventh week of embryonic development in human beings. Then 

 the determination comes, causing normally the modifications of de- 

 velopment to form the organs of one sex or the other. The develop- 

 ment of the external organs of the two sexes is strictly parallel. 



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