W. H. HARRIS ON MARINE MICROSCOPIC VEGETABLE ORGANISMS. 147 



the remains of the cavity may be plainly traced, agreeing with the 

 contour of the fragment ; from this cause the difficulty of ascer- 

 taining the size robust species may attain is increased. 



In some specimens the filaments are tolerably uniform in size 

 throughout their entire length ; others vary, alternately becoming 

 small and large ; others are large for a greater or less distance, 

 then suddenly become small and continue so to the boundary of 

 the particle. 



I have noticed it is easy to associate distinct forms when in 

 close proximity, which then convey the notion of a vesicular body 

 arising fi'om the filament, and should spores be present in the 

 former the illusion is complete. But this appearance may arise 

 in one of two ways : the filament of, say Achlya perforans, may 

 approach the neck-hke portion of, say Lacuna glohosa^ until they 

 become nearly confluent, or the germ of the latter may enter the 

 perforation of the former, and commence its growth from tuithm 

 the empty filament ; the result is practically the same in either 

 case — a false impression is created. Moreover, the false images 

 these plants give rise to, owing to the different planes at which 

 they locate themselves within the particles of shell, etc., provide 

 a fruitful source of error. 



That certain species are provided with processes which sei've 

 the office of reproductive organs I am convinced ; but in the 

 majority the production of spore- like bodies appears to be accom- 

 plished by the simple breaking up of the plasmic matter within 

 the larger parts of the filaments. 



The search for special organs of reproduction - has strongly 

 impressed me with the necessity for seeking isolated specimens in 

 order to avoid incorrect notions regarding this phase in the life- 

 history of the organisms. 



There is a feature which appears to be pretty constant among 

 the majority of species which may be referred to — viz., their habit 

 of not becoming confluent : no matter however thickly crowded 

 together they may be, they persistently avoid contact with each 

 other. I have observed four filaments pursuing a parallel course 

 divided by partitions of shell not wider than the three- thousandth 

 part of an inch, and I once saw an example (unfortunately lost) 

 of a filamentous form similarly avoiding the bulbous portion of a 

 Lacuna globosa for more than half the diameter of- tha: latter, 

 before it passed on in its original course. The cause of this 



