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III. — Note on the Minute Structure of Pelomyxa palustris. 

 By G. Gullivee. 



(Bead 11th January, 1888.) 



This interesting Protozoon was first described by Grreef, and there is 

 a good account of it in Prof. Bay Lankester's article in the ' Encyclo- 

 paedia Britannica.' It is found in mud at the bottom of pools, often 

 in association with Amoebse and other allied forms. It is distinguished 

 by its large size — for it often attains to a diameter of 1/30 in. — its 

 sluggish movements by means of blunt pseudopodia, and its voracity, 

 the protoplasm having in general much foreign matter in it. On 

 looking at living specimens, it struck me that the minute structure 

 was probably more complicated than might at first be imagined ; and 

 the large size of the animal enabled my friend Mr. Pode to cut some 

 sections which form the subject of the few remarks which I wish to 

 make. These sections were exceedingly friable, but portions remain 

 in a sufficiently perfect condition to allow me to demonstrate a few 

 points which I venture to think have not before been sufficiently 

 dwelt upon. My remarks refer first to the exoplasm, and secondly to 

 the endoplasm. 



Exoplasm. — Professor Bay Lankester divides the Protozoa into 

 Gymnomyxa and Corticata, the former containing, besides many other 

 forms, Amoeba, and the genus which is the subject of these remarks, 

 and the latter the higher Protozoa only. The distinction which he 

 makes between the two groups rests upon the statement that a 

 definite cortical layer is present only in the latter. He says, " The 

 distinction into so-called exoplasm and endoplasm recognized by 

 some authors is not founded on a permanent differentiation of sub- 

 stance, but is merely due to the centripetal aggregation of granules 

 lying in a uniform undifferentiated protoplasm. This may be true of 

 many forms, but the sections under the Microscope show that not 

 only is there in Pelomyxa a distinction into exoplasm and endoplasm, 

 but that the two, instead of passing into one another gradually, as 

 one would have expected, are sharply defined by a definite boundary, 

 without transitional phases of structure. The exoplasm forms a 

 complete investment to the endoplasm in the form of a layer of 

 uniform thickness apparently composed of delicately reticulated firm 

 protoplasm, containing small vacuoles, and, as I think, devoid of 

 nuclei, such few as are seen being apparently pushed on to its sub- 

 stance from the endoplasm beneath. In the process of hardening, 

 this layer readily separates from the subjacent softer endoplasm. 

 Here and there a large vacuole, and in some cases a diatom or other 

 foreign body can be seen in its substance. 



Endoplasm. — This is evidently much softer, more friable, and 

 has its parts more loosely held together than the outer layer. Prof. 

 Lankester speaks of it as composed of a richly vacuolated protoplasm, 



