70 THE NATURAL HISTOEY EEYIEW. 



The other organs are small sacs inserted on the hairs which line 

 the walls of the cavities. The sacs contain a number of hya- 

 line corpuscles, enclosing a red granule, which, after their escape 

 from the sac, move rapidly in the water by means of two vibratile 

 cilia. Some EucacesB are diaecious, others hermaphrodite. Por in- 

 stance, Fucus serratuSf L., JFucus vesictdostcs, L., and Fucus 

 nodosuh', L. are diaecious, Fucus platy carpus, Thur., Fucus canali- 

 culatus, L. and Fucus tuherculatus, Huds. are hermaphrodite. Fucus 

 vesiculosuSf L. is the species to which M. Thuret has devoted the 

 most attention, and his account of his observations and experi- 

 ments is shortly as follows : — An examination of the young female 

 conceptacles of this species shows that the sporangia originate in 

 small protuberances forming the wall of the cavity. These mamillse, 

 which are at first unicellular, become bi-cellular by the formation 

 of a transverse septum, the upper one of the two cells thus formed 

 becomes the sporangium, the lower one the pedicel. The dark 

 coloured contents of the sporangium at length divide into eight 

 segments, and by the rupture of the sporangium the divided body or 

 " octospore," escapes, enclosed in a hyaline membrane (epispore) 

 which keeps the eight segments closely pressed together. "Within 

 the epispore is another extremely delicate membrane extending over 

 the octospore. By the dissolution of the upper portion of the 

 octospore and the rupture of the delicate membrane just mentioned, 

 the octospore becomes free, and separates into eight spherical spores 

 which have no integument. Thus far the observations have 

 reference to the female organs. The process which takes place 

 in the male fronds is very similar. The small sacs or antheridia 

 become detached from the walls of the conceptacle and escape in 

 vast quantities through the orifice of the latter. Shortly after 

 their escape they burst and emit swarms of spermatozoa, which 

 move about in sea water with great rapidity, their motion lasting 

 sometimes for upwards of two days. 



When the spores and spermatozoa, are placed in water together, 

 the latter attach themselves to the former in great numbers, and 

 by means of their vibratile cilia communicate a motion of rotation 

 sometimes extremely rapid.* After lasting for a time, but rarely 



* M. Thuret does not consider this rotation to be of much importance, for 

 although seen plainly enough under the microscope he thinks it never occurs in 

 pature, and that it is in no way necessary for impregnation. The fact of its 



