FOUND IN TI IE COELOM OF SAGITTA. 



the cential non-plasmic substance. The cytoplasm is differentiated, though 

 by no means sharply into the ectoplasm and the entoplasm. The former 

 forms a very thin, uniformly finely granular superficial layer, while the 

 latter is a little thicker and presents a reticulate granular appearance (fig. 3). 

 The two layers show neither a structural delimitation between them nor 

 differential staining properties. 



The curious réfringent layer we have seen in the fresh state, when 

 examined in sections, presents itself as being made up of a series of deeply 

 stained pieces arranged in a layer in the deepest parts of the entoplasm. A 

 cursory examination of stained total preparations or of serial sections makes 

 it at once clear that the layer in question consists in fact of comparatively 

 thick threads which divide and anastomose, so as to bring about a network 

 with close and irregular-shaped meshes. The substance of the threads is 

 evidently the chromatin, and I take no heed in regarding the entire structure 

 as the meganucleus of the organism. The entire meganucleus may thus be 

 said to have the structure of a basketwork with a spacious hollow inside. 

 Strikingly remarkable as is this feature ot the meganucleus, it may probably 

 be regarded to be a condition which is foreshadowed more or lass in some 

 other astomatous ciliates, c. g., Rhizocariian concai us Caullf.kv & Mesnil 

 Anoplophrya alluri Cépède, Opaliiioßsis sepiolae Foettinger, etc. 



The meganuclear threads are seen in most parts to be surrounded by 

 narrow empty spaces, which are always found to be bordered each by a 

 distinct and dense sheet of the entoplasm. I therefore regard the spaces 

 to be equivalent to the excretory vacuoles described by Metcalf 1 ' from a 

 number of Opalina species. 



The part of the entoplasm lying internal to the meganuclear threads 

 appears in sections as an extremely thin, very finely granular and deeply 

 staining layer which directly invests the large central non-plasmic body. 

 Fig. 3, which represents under a high magnification a small portion of a 

 section belonging to the same series as that of fig. 2, illustrates all the 



1) Metcal , M.M.— The excretory organs of Opalina, Parts I and II. Arch. 1. Protist., Band X, 

 1907. 



