540 Transactions of the Society. 



lowing spring. The name of " durable eggs " (Dauereier, Cohn), 

 expresses better their physiological character, of opening only after 

 a long period of repose. 



Some days before hatching we can distinguish in the egg a well- 

 formed embryo, and recognize the greater part of the organs. It 

 is doubled upon itself, the head and tail curved on the ventral face, 

 and in contact with one another (Fig. 12). Just before hatching 

 it moves energetically, and turns round in all directions, vibrating 

 its buccal ciha. These movements are to break the shell of the 

 egg. The young animal escapes out of the opening, and soon 

 afterwards the margins of the opening join so exactly that the 

 envelope (absolutely empty) seems intact. The newly hatched 

 young are vermiform and from O'lO mm. to 0-12 mm. in length 

 (Fig. 10). 



IV. — The Galls of Vaucheria terrestris. 



We must now consider the excrescences of the Vaucheria, and 

 try to decide whether or not they ought to be assimilated to the 

 galls produced by the action of some insects on phanerogamous 

 plants. 



F. terrestris is composed of tubular filaments, without internal 

 septa, and filled with green matter. The organs of fructification, 

 the antheridium and the sporangium, are borne on a small secondary- 

 branch rising at right angles from the side of the principal fila- 

 ment (Figs. 14, 15). This common branch is itself divided into 

 two branches, the inferior of which is bent downwards in the shape 

 of a horn, bearing the antheridian cell at its extremity. The 

 superior, which is the continuation of the secondary branch, becomes 

 club-shaped at the summit, and terminates in a transversal j)artition 

 to form the oogone or sporangium. 



Passing from the organs of reproduction to the excrescences 

 inhabited by N. Wernechii, a simple comparison will show the 

 complete morphological identity of the two. The parasitic cysts are 

 only the persistent branches which bore the organs of reproduction, 

 and which under the influence of the parasite have enlarged con- 

 siderably and modified their form. We sometimes find young 

 rotifers lodged in capsules which in no wise differ in form and size 

 from the normal sporiferous branches (Fig. 15, rs), which removes 

 all doubt concerning the nature of these productions. 



As the parasite grows, the capsule which encloses it sometimes 

 increases to five times its original bulk (Figs. 16, 17, and 18). At 

 the same time the wall of cellulose thickens over all the periphery. 



It is always at a very early age that the parasite is introduced 

 into the plant, to pass there the remainder of its life. It is nourished 

 exclusively on the colourless plasma of the capsule, as is seen by the 

 entire absence of green colour in the digestive tube. This confirms 



