REPRODUCTION. 151 



we owe the statement to able and trustworthy inquirers, it is yet to be desired tliat we had further 

 verification of a fact so much at variance with the phenomena of gemmation as presented elsewhere 

 among the Hydroida. 



It is rarely that the medusa has been noticed to emit buds simultaneously with the produc- 

 tion of ova or spermatozoa. Instances, however, are on record in which the sexually mature 

 medusa has also multiplied itself by budding. This has been observed by Rusch' in a medusa 

 which he refers to the Sarsia prolifera of Forbes, and in which the basal I)ulbs of the tentacles 

 gave origin to medusa-buds, which were coexistent with the presence of generative elements in 

 the walls of the manubrium ; by Krohn" in the medusa of Clavalella, which he has seen to be 

 loaded with ova at the same time that medusa-buds were emitted from the margin of its umbrella; 

 and by Sars,' who in a blastocheme {Thaumantias multicirratus, Sars) saw medusae budding from 

 the radiating canals simultaneously with the existence of the convoluted generative pouches. 



No multiplication by budding has ever been noticed in the sporosac, a zooid which, it is to 

 be borne in mind, is almost from its first appearance engaged in the production or protection of 

 the generative elements. 



Fission. — Though budding thus constitutes a highly characteristic and all but universal phe- 

 nomenon among the Hydroida, multiplication by spontaneous fission is, on the other hand, rare 

 and exceptional. Kolliker* observed a process of true fissiparous multiplication in a medusa {Stomo- 

 hracMum mirahile, Koll.) obtained in abundance at Messina. The fission always connuenced by a 

 vertical division of the manubrium, which thus became doubled ; and this stage of the process was 

 followed by a similar division of the umbrella, separating the animal into two independent halves. 

 The process, however, did not stop here, but was followed by a further division of each of the 

 two first-formed segments into two others, by a fission at right angles to the direction of the first ; 

 while Kolliker's observations led him still further to conclude that the process does not terminate 

 with even the second cleavage, but, on the contrary, that it still goes on, the animal continuing 

 to multiply itself by frequent acts of fission. 



Developed generative bodies were not observed in Stomohrachium mirahile, and Kolliker is 

 of opinion that this medusa is only the young of another {Mesonema carulcscens, Koll.) found in 

 the same seas, and in which no division takes place, but in which well-developed generative sacs 

 occur along the course of the radiating canals. 



But besides this case of fissiparous multiplication in the medusa 1 am enabled to give a 

 very well-marked and interesting one which I met with in the trophosome of an undescribed 

 campanularian hydroid (woodcut, fig. Gl), to which I have assigned the name Schizocladiinu 

 ramosum." 



I have not as yet met with this hydroid more than once. It is a profusely branched form, 

 with its trophosome having much resemblance to that of Obelia dickotoma ; but as no gonosome 



' Busch, ' Beobaclit. iiber Anat. u. Entwick. einiger ■wirbellosen Seethicrc,' p. 1, pi. i, fig. 1. 



' Krohn, ' Wiegmann's Arcliiv,' 1861. In the gemmiferous specimens of the Clavalella medusa 

 examined by myself, there were no visible generative elements. 



' Sars, ' Bescrivelser.' 



* ' Zoologische Beitrage, 1861.' 



° "On a Mode of Reproduction by Spontaneous Fission in the Hydroida." ' Reports of Brit. 



Assoc, for the Advancement of Science,' 1870. 



