324 PROFESSOR MARSHALL. 



THE MORPHOLOGY OF THE SEXUAL ORGANS OF HYDRA. 



By A. Milnes Marshall, M.D., D.Sc, Beyer Professor of Zoology 

 in Oivens College. 



Hydra stands alone, or almost so, among Hydrozoa, inasmuch as its 

 reproductive organs, whether ovaries or testes, develop and ripen in 

 the body-Avail of the animal instead of in special buds or gonophores. 

 Concerning the relationship in this respect between Hydra and other 

 Hydrozoa two diametrically opposite views have been held, one being 

 that Hydra exhibits the simplest and most primitive condition of the 

 reproductive organs, prior to the evolution of special sexual buds ; the 

 other that the condition in Hydra is one of extreme degeneration, the 

 sexual buds that were previously present having become completely 

 aborted. 



A short time ago, Professor Weismann of Freiburg published some 

 extremely interesting and valuable researches on the development of 

 the sexual products in Hydrozoa, 1 and it is the object of the present 

 paper to enquire into the bearing of these results on the problem 

 stated above concerning Hydra. 



In one of the typical hydroid colonies such as Podocoryne or Bou- 

 gainvillea the sexual products, whether ova or spermatozoa, are con- 

 tained in medusoid buds, and do not ripen until these meduste have 

 attained full development, and detached themselves from the colony 

 so as to lead a free-swimming existence. In many cases, however, the 

 sexual products ripen before the medusoid bud has completed its de- 

 velopment, in which case the bud remains attached to the colony in 

 1 Weismann, Die Entstehung der Sexualzellen bei den Hydromedusen. Jena, 1883, 



