642 EDWARD T. BROWNE. 



Allman, in 1871; gave an account, with figures, of repro- 

 duction by spontaneous fission in a Hydroid which he named 

 Schizocladiuni ramosum. Although Allman had Avorked 

 for many years upon British Hydroids, yet he had never 

 before mot with a case of fission amongst them. Hincks^ in 

 1872, found Campanularia neglecta reproducing by 

 fission in a similar manner, and refused to accept Allman's 

 new genus Schizocladium, " which seems to rest on a single 

 character, the development of fission-frustules in a certain 

 Avay — a character which, there is reason to believe, may 

 have a wide range amongst the Hydroida." Hincks suggests 

 that Allman^s Schizocladiuni is probablyan Obelia, AUman 

 found the colony in Loch Long (Firth of Clyde), and states that 

 it bore a considerable resemblance to that of Obelia di cho- 

 toma. It was without gonosomes, and it was the absence of 

 the gonosomes that led Allmau to establish a new genus for a 

 Hydroid that was reproducing by fission. AUman states that 

 the frustule on liberation has a distinct endoderm and ecto- 

 derm, but no perisarc. It has no means of locomotion, and 

 attaches itself by a mucous excretion from its surface to the 

 glass of an aquarium. Soon after attachment the raucous 

 excretion forms round the fission-frustule a very thin tube, 

 which is the perisarc. Once attached a hydranth develops 

 from it, then later on other hydrantlis are formed and a little 

 colony arises by branching. 



Fission is not merely the nipping off a small portion of the 

 cocnosarc, as the fission-frustule contains all the elements neces- 

 sai'y for the formation of a new colony. It does not usually 

 take place at the same time as sexual reproduction. In Micro- 

 hydra the method of fission is different from that in 

 marine Hydroids, as there are no branches. An outgrowth 

 takes place from the side of the hydranth (PI. 36, fig. 21), 

 and this is nipped off and develops into a hydranth. 



It is very probable that the Hydroid of Limnocodiuni 

 also reproduces asexually by fission. Parsons, wlio kept the 

 Hydroids in an aquarium, states " that the polyps made their 

 appearance on the side of a sponge which had been in contact 



