278 DESCiiiPTioN OF \ Polygastrica. 



internal membrane of the cell- wall becomes enlarged at the suture or 

 line of separation, and projects in tbe form of an iiTegular cone, with 

 a blunt or rounded apex forming a beak, whose side view presents a 

 triangular outline. This beak becomes filled with cndochrome, 

 either by the dilatation or increase of the contents of the half-frond, 

 and the divided frond assumes the appearance of one with two im- 

 equal segments (f. 12.) being what M. Morren calls "a Closterium 

 of two unequal cones." On these membranous expansions, at the 

 concave surfaces of the fronds, and close to the original sutm'es, there 

 appeal', almost simultaneously with the formation of the beaks, two 

 circular projections, which, rupturing at their apices, give egi-ess to 

 the delicate sacs which enclose the endochrome, and which, drawing 

 with them their contents, and meeting with the endochrome sacs 

 emitted through similar projections from the other half fronds, form, 

 by their connection, irregular masses, which quickly consolidate and 

 assume the appearance of perfectly, circular, smooth, dark-coloured 

 balls, the sporangia of Ealfs and seminules of Mon-en. (P. 18, 

 f. 13 and 14.) 



" The discharge of the endochrome and formation of the sporangia 

 are accomplished with much rapidity, and may often be seen taking 

 place in the field of the microscope, the whole operation not occupy- 

 ing more than a few minutes. It -wall be seen from an inspection of 

 the figures, that during the formation of the sporangia there appears 

 to be a second development of mucus in the form of rings around the 

 reproductive bodies ; this is probably only the efi'ect of the pressure 

 produced by the growth of the sporangia on the mass of investing 

 mucus. It will also be seen that the pale transverse band adopted 

 by Ealfs as a characteristic of the genus Closterium, and which in 

 figs. 10 and 11 occupies the centre of the undivided frond, is, upon 

 self-division taking i)lacc, removed a little towards the extremities 

 of the half fronds. The reason, as weU as the cause of this motion, I 

 am unable to explain, but it seems to confirm the propriety of adopt- 

 ing the band itself as a permanent and important character. 



" With regard to the subsequent changes which take place in the 

 sporangia, the time which elapses before they produce young fronds, 

 and the mode in which such evolution of a fresh race is accomplished, 

 I have not been fortunate enough to ascertain with any certainty. . , . 



