Origin of Sex. 297 



thai we ordinarily meet with are hermaphrodites, but a considerable 

 11 umber are unisexual, one plant bearing the fertilizing pollen, and an- 

 other, the ovules, which when fertilized grow into the seed. The lowest 

 plants are asexual like most of the lowest animals. The following com- 

 prise most of the hermaphrodite animals, those of a lower grade than 

 these being asexual, and those of higher organization unisexual : 



Some Fponoes are Hermaphrodite, others unisexual. " But among the latter it is not 

 uncommon to find ( e. g., in Sycandra raphanus) that the production of one set of ele- 

 ments preponderates over the other, and thus we have hermaphrodites with a distinctly 

 male or female bias. In other words, thev are verging towards unisexuality." 1 



( ' Ir literates. The members of this class are higher in having the production of the 

 sex cells more restricted to definite regions, tissues, organs, or even persons. "The highly 

 active Ctenophores, like Bertie, are all hermaphrodite, and that very closely. On one 

 side of the meridional branches of the alimentary canal ova arise, on the other side, 

 spermatozoa." Some sea-anemones and corals are hermaphrodite. In the case of Coral- 

 Hum ( the red coral ) " the whole colony may he unisexual, or one branch of the colony, 

 or only certain individuals on a branch, while genuine hermaphroditism of individual 

 polyps also occurs. Among hydrozoa ( zoophytes, swimming-bells, jelly-fish) hermaph- 

 roditism is a rare exception, or we may almost say reversion. The common hydra, 

 which is a somewhat degenerate type, is hermaphrodite, though at the same time indi- 

 viduals may be found with only ovary or only testes." 



Worms. Among these, the turbellarians are all hermaphrodite except two genera ; 

 the trematodes or flukes are likewise hermaphrodite, except one or two genera; the ces- 

 todes, or tape-worms, are all hermaphrodite. These are parasites. Most nemerteans are 

 unisexual, but some are hermaphrodite; all leeches are hermaphrodite; the thread- 

 worms, or nematodes, are all hermaphrodite except one genus Angiostomum. This an- 

 imal has a reproductive gland which first produces spermatozoa and afterwards ova, 

 which are fertilized by them. Of the higher annelid worms the Protodrilus is herma- 

 phrodite and so are the earth-worms, but the marine-worms are unisexual except one 

 genus, the Sagitta. Echinoderms are all unisexual except one brittle star and one genus 

 of sea-slugs (Synapta). Arthropods. Barnacles are mostly hermaphrodite, but most 

 crustaceans are unisexual. In the Cymothoidae (Isopods) the sexual organ is male 

 while the animal is young, but becomes female later in life. Myriopods are unisexual, 

 and so are insects, with one exception. Mollusks. Oysters, clams, cockles, &c., are her- 

 maphrodite, but most other bivalves are unisexual. Of snails, or gasteropods, the 

 Ktreptoneura, or twisted nerves, are of separate sex, but the straight-nerved Euthyneura 

 are hermaphrodite. Pteropods are hermaphrodite; Scaphopods, or Elepliant's-tooth 

 shells, are unisexual, and so are the Cuttle fishes. 



There are many casual instances of individual hermaphroditism amongst tribes \isu- 

 ally unisexual. They are doubtless due to arrested development. They are occasional 

 amongst birds and mammals, such conditions usually resulting in sterility. They ap- 

 pear to be tolerably common among the amphibians. "Thus Marshall notes that the 

 testes of a common frog may be associated with genuine ova, or an ovary may occur on 

 one side, and a testis with an anterior ovarian portion upon the other. Bourne gives the 

 case of a frog with the ovary well developed on the right side, and opposite this an ovary 

 anteriorly replaced by testis. One of the toads ( Pelobates fuscus ) seems to be frequently 

 hermaphrodite, the male being furnished with a rudimentary ovary in front of the tes- 

 tis. A similar hermaphroditism is not at all infrequent in cod, herring, mackerel, and 

 many other fishes; while slightly lower down in the series it occurs in the hag-fish 

 (i1/?///r), sometimes a fish is male on one side, female on the other, or male anteriorly 

 and female posteriorly." "Among invertebrates the same has been occasionally ob- 

 served, especially among butterflies, where striking differences hi the coloring of the 

 wings on the two sides have, in some cases, been found to correspond to an internal co- 

 existence of ovary and testis." - Lobsters have been found with similar internal arrange- 

 ment, and something analogous has been observed in a Deer. Traces of hermaphrodit- 

 ism in man are shown in his rudiment called the male uterus, and in woman in the rudi- 

 ment called the parovarium. ( See fig. 30.) 



Although hermaphrodites possess both the sexual elements in one 



1 " Evolution of Sex," (jexldes and Thomson, 70. 



66. 



