NOTES AND MEMORANDA. 93 



becoming slender and flattened like the new or posterior peristome. 

 Afterwards, both peristomes increase in length and breadth, so that at 

 the end of the process they are both in the saiae stage. The new 

 caudal cilia always arise, as Stein made out in Stijlonichia, on the 

 dorsal side : the prfeoral cilia and undulating membrane are formed 

 anew, the old ones being absorbed. The adoral cilia or membranelles 

 are probably directly transformed, like the peristome, into those of the 

 new individual. The new cilia all exhibit a sort of clumsiness of 

 movement, quite different to the facility of their adult motions. 



The author remarks that the process of division in Oxytrichina is 

 not one of true fission, but is rather one of bud-formation. 



In an appendix Sterki gives the characters of some new genera and 

 species he has established. The new genera are Histrio ( = Stylonichia 

 hisfrio), Amphisia, and Gonosfomum (separated from Oxytricha), Stylo- 

 nethes, Allotricha, Strongylidium, and Trichocj aster. 



The Sexual Process in Diatoms. — An article on this question, con- 

 taining a discussion on the sexual process in general, occurs in ' Der 

 Naturforscher ' for November 23, 1878. The writer begins by a 

 statement of the five methods in which the auxospores of Diatomacete 

 are known to be formed : these are the following : — 



1. A single individual throws off both valves, secretes a mucila- 

 ginous investment, extends itself, and grows. The auxospore tlius 

 formed surrounds itself with a thin membrane devoid of silica, and 

 within this secretes the usual pair of siliceous valves, thus forming the 

 "firstling-cell" (Erstlingzelle) of a new generation. 



2. The protoplasm of a cell divides into two naked daughter-cells, 

 which make their way out of the mother-cell, and form an auxospore. 



3. Two individuals, lying close to one another, secrete an invest- 

 ment of mucilage : both these throw off their valves, and so form a 

 pair of naked cells lying in close proximity to one another, but 

 without actually touching. Both of these extend parallel to one 

 another in the direction of their length until they attain the normal 

 size of auxospores ; outside these a thin membrane (perizonium) is 

 found, and within this the ordinary siliceous valves. 



4. Two individuals, generally surrounded by a gelatinous invest- 

 ment, throw off their old valves, and coalesce into a single naked mass 

 of protoplasm, which grows into a single auxospore. 



5. Two individuals, again surrounded by mucilage, throw off their 

 old valves, and each divides transversely into two naked daughter- 

 cells, each of which then coalesces with the corresponding daughter- 

 cell of the other individual. Two naked zygospores are thus formed, 

 each of which becomes an auxospore, and subsequently, by the forma- 

 tion of siliceous valves, a firstling-cell. 



Of these five methods the fourth and fifth are certainly sexual, 

 being a process of zygospore-formation. The fii'st mode is as certainly 

 asexual, a process of cell-formation by rejuvenescence, so tLat in the 

 single group of Diatomacece. the auxospores, by which a new generation 

 is started, may be produced either sexually or asexually. 



The second mode requires further investigation : about the third 

 there is a diflSculty ; it is a pi'ocess of rejuvenescence, taking place, 



