14 



PKOTOZOA 



out into very short fine filaments. Scattered in the protoplasm are 

 a number of minute cylindrical crystals, of unascertained composi- 

 tion. Pelomyxa is of very large size for a Protozoon, attaining a 

 diameter of T \th of an inch. It takes into its substance a quantity 

 of foreign particles, both nutrient organic matter such as Rotifera 

 and Diatoms and sand particles. It occurs not uncommonly in old 



FIG. V. Litham&ba discus, Lank, (after Lankester, 34). A, quiescent ; B, 

 throwing out pseudopodia. c.v., contractile vacuole, overlying which the 

 vacuolated protoplasm is seen ; cone, concretions insoluble in dilute HC1 

 and dilute KHO, but soluble tn strong HC1 ; n, nucleus. 



muddy ponds (such as duck-ponds), creeping upon the bottom, and 

 has a white appearance to the naked eye. Lithamceba (Fig. V.) is 

 distinguished by its large size, disk-like form, the disk-like shape of 

 its pseudopodia, the presence of specific concretions, the vacuolation 

 of its protoplasm, and the block-like form and peculiar tessellated 

 appearance of its large nucleus, which has a very definite capsule. 

 In Lithamceba it is easy to recognize a distinct pellicle or temporary 

 cuticle which is formed upon the surface of the protoplasm, and 

 bursts when a pseudopodiuin is formed. In fact it is the rupture of 

 this pellicle which appears to be the proximate cause of the outflow 

 of protoplasm as a pseudopodium. Probably a still more delicate 

 pellicle always forms on the surface of naked protoplasm, and in the 

 way just indicated determines by its rupture the form and the 

 direction of the "flow" of protoplasm which is described as the "pro- 

 trusion" of a pseudopodium. 



The shells of Lobosa Testacea are not very complex. That of 

 Arcella is remarkable for its hexagonal areolation, dark colour, and 

 firm consistence ; it consists of a substance resembling chitin. 

 That of Difflugia has a delicate membranous basis, but includes 

 foreign particles, so as to resemble the built-up case of a Caddis 

 worm. 



Arcella is remarkable among all Protozoa for its power of secret- 

 ing gas-vacuoles (observed also in an Amoeba by Biitschli), which 

 serve a hydrostatic function, causing the Arcella to float. The gas 

 can be rapidly absorbed by the protoplasm, when the vacuole neces- 

 sarily disappears and the Arcella sinks. 



CLASS IV. LABYRINTHULIDEA. 



Characters. Gymnomyxa forming irregular heaps of ovoid 

 nucleated cells, the protoplasm of which extends itself as a branching 

 network or labyrinth of fine threads. The oval (spindle-shaped) 

 corpuscles, consisting of dense protoplasm, and possessing each a 

 well-marked nucleus (not observed in Chlamydomyxa), travel regu- 

 larly and continuously along the network of filaments. The oval 

 corpuscles multiply by fission ; they also occasionally become 

 encysted and divide into four spherical spores. The young forms 

 developed from these spores presumably develop into colonies, but 

 have not been observed. 



Genera. Two genera only of Labyrinthulidea are known : 

 liabyrinthula, Cienkowski ; Chlamydomyxa, Archer. 



Cienkowski (35) discovered Labyrinthula on green Algae growing 

 on wooden piles in the harbour of Odessa (marine). It has an 

 orange colour and forms patches visible to the naked eye. Chlamy- 

 domyxa was discovered by Archer of Dublin (36) in the cells of 

 Sphagnum and crawling on its surface ; hence it is a freshwater 

 form. Unlike Labyrinthula, the latter forms a laminated shell of 

 cellulose (Fig. VI. 2, c), in which it is frequently completely 

 enclosed, and indeed has rarely been seen in the expanded 

 labyrinthine condition. The laminated cellulose shells are very 

 freely secreted, the organism frequently deserting one and forming 

 another within or adherent to that previously occupied. The 

 network of Chlamydomyxa appears to consist of hyaline threads of 

 streaming protoplasm, whilst that of Labyrinthula has a more 

 horny consistence, and is not regarded by Cienkowski as protoplasm. 



The spindle-shaped cells are much alike in form and size in the 

 two genera; but no nucleus was detected by Archer in those of 

 Chlamydomyxa. The encysting of the spindle-cells and their 

 fission into spores has been seen only in Labyrinthula. Chlamy- 

 domyxa is often of a brilliant green colour owing to the presence of 

 chlorophyll corpuscles, and may exhibit a red or mottled red and 

 green appearance owing to the chemical change of the chlorophyll. 



It has been observed to take in solid nourishment, though Labyrin- 

 thula has not. 



The Labyrinthulidea present strong resemblances to the Myceto- 

 zoa. The genus Dactylostelium (Sorophora) would come very close 

 to Labyriiithula were the amceba? of its aggregation plasmodium 



FIG. VI. Labyrinthulidea. 1. A colony or "cell-heap" of Lalnjrinthula 

 vitellina, Cienk., crawling upon an Alga. 2. A colony or "cell-heap" 



of Chlamydomyxa labyrinthuloides, Archer, with fully expanded network 

 of threads on which the oat-shaped corpuscles (cells) are moving, o is an 

 ingested food particle ; at c a portion of the general protoplasm has 

 detached itself and become encysted. 3. A portion of the network of 



Labyrinthula vitellina, Cienk., more highly magnified, p, protoplasmic 

 mass apparently produced by fusion of several filaments ; p', fusion of 

 several cells which have lost their definite spindle-shaped contour; s, 

 corpuscles which have become spherical and are no longer moving (perhaps 

 about to be encysted). 4. A single spindle cell and threads of Laby- 



rinthula macrocystis, Cienk. n, nucleus. 5. A group of encysted cells 



of L. macrocystis, embedded in a tough secretion. 6, 7. Encysted cells 



of L. macrocystis, with enclosed protoplasm divided into four spores. 

 8. 9. Transverse division of a non-encysted spindle-cell of L. macrocystis. 



set upon a network of threads. Such a network, whether in the 

 condition of soft protoplasm or hardened and horny, is represented 

 in the higher Mycetozoa by the capillitium of the sporocysts. 



The most important difference between Archer's Chlamydomyxa 

 and Cienkowski's Labvrinthula is that in the former the threads 



