ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 289 



differentiated from the cortex, and filled with chromatophores. The 

 epidermis is the chief assimilating organ. The growing point lies in 

 a funnel-shaped depression at the apex of the branch. The barren 

 conceptacles are formed on the young branches in acropetal suc- 

 cession ; a bundle of paraphyses projects from their ostiole ; and 

 these are continually renewed as the old ones are rubbed off. No 

 transitional structures were observed between the barren and fertile 

 conceptacles. The air-bladders are formed by strong tangential 

 growth of the cortex and epidermis ; the central tissue remaining 

 unaffected. A large number of barren, but only a few fertile con- 

 ceptacles are found on the air-bladders. 



The sexual organs are formed from November to May in the solid 

 warty cartilaginous conceptacles ; these are from a few millimetres to 

 2 or 3 centimetres in length, and are usually brightly coloured. The 

 fertile, like the barren conceptacles, are formed in acropetal suc- 

 cession, and have a circular ostiole. The parts of the wall nearest to 

 the ostiole develope a large number of branched antheridial hairs 

 with a few paraphyses ; large quantities of oogonia springing from 

 the base, surrounded also by paraphyses. Occasionally some of the 

 conceptacles are unisexual. 



After the escape of the antheridia from the conceptacle, they lie 

 before the ostiole in an orange-coloured heap : the oogonia, on the 

 contrary, never collecting round the ostiole. The ripe antheridia are 

 somewhat curved, and the antherozoids are formed in them with great 

 rapidity by bipartition. In Cystosira the wall of the antheridium 

 consists of only one layer of cells, the entire antheridium escaping 

 through the ostiole ; while in other Fucacese the wall consists of two 

 layers which separate from one another, and the inner layer only, 

 with the antherozoids, escapes through an opening in the outer. The 

 antheridia are specifically heavier than sea-water, and are frequently 

 caught when sinking by the tuft of paraphyses projecting from the 

 ostiole of the barren conceptacles ; the antherozoids then escaping by 

 the conversion into mucilage of their investing membrane. They are 

 curved and pear-shaped, and contain a colourless corpuscle (nucle- 

 olus ?) and an orange-coloured eye-spot ; they have two cilia of 

 unequal length. The swarming takes place chiefly in the fore- 

 noon. 



The oogonia are usually sessile and have a distinct nucleus ; they 

 are of an olive-brown colour with light-coloured apex. The membrane 

 consists of two layers, both becoming gelatinous when ripe ; the 

 nucleus divides in two ; the lower portion becomes the true ovum- 

 nucleus, and the upper portion is expelled as the " excretion-sub- 

 stance." In the act of impregnation a number of the antherozoids 

 force themselves into the gelatinous envelope of the oosphere ; the 

 cubic contents of the latter exceeding that of a single antherozoid 

 40,730 times. The actual contact of the antherozoids with the pro- 

 toplasm of the oosphere was not observed ; but apparently the 

 entrance of a single antherozoid is sufficient to cause the excretion 

 of a cellulose membrane ; the gelatinous envelope disappearing at the 

 same time. Impregnation usually takes place while the oospheres 



Ser. 2.— Vol. VI. U 



