PROTOZOA 



23 



which are totally devoid of skeleton. Similarly it does not appear 

 to be a matter of great significance that some forms (Polycyttaria) 

 form colonies, instead of the central capsules separating from one 

 another after fission has occurred. 



It is important to note that the skeleton of silex or acanthin 

 does not correspond to the shell of other Gymnomyxa, which 

 appears rather to be represented by the membranous central cap- 

 sule. The skeleton does, however, appear to correspond to the 

 spicules of Heliozoa, and there is an undeniable affinity between 

 such a form as Clathrulina (Fig. VII. 2) and the Sphserid Peripylaea 

 (such as Heliosphsera, Fig. XIV. 14). The Radiolaria are, however, 

 a very strongly marked group, definitely separated from all other 

 Gymnomyxa by the membranous central capsule sunk in their proto- 

 plasm. Their differences inter~se do not affect their essential struc- 

 ture. The variations in the chemical composition of the skeleton and 

 in the perforation of the capsule do not appear superficially. The 

 most obvious features in which they differ from one another relate to 

 the form and complexity of the skeleton, a part of the organism so 

 little characteristic of the group that it may be wanting altogether. 

 It is not known how far the form-species and form-genera which 

 have been distinguished in such profusion by Haeckel as the 

 result of a study of the skeletons are permanent (i.e., relatively 

 permanent) physiological species. There is no doubt that very 

 many are local and conditional varieties of a single Protean species. 

 The same remark applies to the species discriminated among the 

 shell-bearing Reticularia. It must not be supposed, however, that 

 less importance is to be attached to the distinguishing and record- 

 ing of such forms because we are not able to assert that they are 

 permanent species. 



The yellow cells (of spherical form, '005 to 0'15 of a millimetre 

 in diameter) which occur very generally scattered in the extra- 

 capsular protoplasm of Radiolaria were at one time regarded as 

 essential components of the Radiolarian body. Their parasitic 

 nature is now rendered probable by the observations of Cien- 

 kowski (43), Brandt (44), and Geddes (45), who have established 

 that each cell has a cellulose wall and a nucleus (Fig. XIV. 6 to 13), 

 that the protoplasm is impregnated by chlorophyll which, as in 

 Diatoms, is obscured by the yellow pigment, and that a starch- 

 like substance is present (giving the violet reaction with iodine). 

 Further, Cienkowski showed, not only that the yellow cells multiply 

 by fission during the life of the Radiolarian, but that when isolated 

 they continue to live ; the cellulose envelope becomes softened ; 

 the protoplasm exhibits amoeboid movements and escapes from the 

 envelope altogether (Fig. XIV. 13) and multiplies by fission. 

 Brandt has given the name Zooxanthella nutricola to the parasitic 

 unicellular Alga thus indicated. He and Geddes have shown that a 

 similar organism infests the endoderm cells of Anthozoa and of 

 some Siphonophora in enormous quantities, and the former has been 

 led, it seems erroneously, to regard the chlorophyll corpuscles of 

 Hydra viridis, Spongilla, and Ciliata as also parasitic Algae, for 

 which he has coined the name Zoochlorella. The same arguments 

 which Brandt has used to justify this view as to animal chlorophyll 

 would warrant the creation of a genus " Phytochlorella " for the 

 hypothetical Alga which has hitherto been described as the 

 "chlorophyll corpuscles" of the cells of ordinary green plants. 



Zooxanthella nutricola does not, for some unknown reason, infest 

 the Acanthometridea, and it is by no means so universally present 

 in the bodies of the Silico-skeleta as was supposed before its 

 parasitic nature was recognized. 



The streaming of the granules of the protoplasm has been observed 

 in the pseudopodia of Radiolaria as in those of Heliozoa and 

 Reticularia ; it has also been seen in the deeper protoplasm ; and 

 granules have been definitely seen to pass through the pores of the 

 central capsule from the intracapsular to the extracapsular pro- 

 toplasm. A feeble vibrating movement of the pseudopodia has 

 been occasionally noticed. 



The production of swarm-spores has been observed only in 

 Acanthometra and in the Polycyttaria and Thalassicollida;, and 

 only in the two latter groups have any detailed observations been 

 made. Two distinct processes of swarm-spore production have 

 been observed by Cienkowski (43), confirmed by Hertwig (46) dis- 

 tinguished by the character of the resulting spores which are ] 

 called " crystalligerous " (Fig. XIV. 15) in the one case, and "di- 

 morphous" in the other (Fig. XIV. 16). In both processes the 

 nucleated protoplasm within the central capsule breaks up by a 

 more or less regular cell-division into small pieces, the details of 

 the process differing a little in the two cases. In those individuals 

 which produce erystalligerous swarm-spores, each spore encloses a 

 small crystal (Fig. XIV. 15). On the other hand, in those indi- 

 viduals which produce dimorphous swarm-spores, the contents of 

 the capsule (which in both instances are set free by its natural 

 rupture) are seen to consist of individuals of two sizes " macro- 

 spores" and " microstores," neither of which contain crystals 

 (Fig. XIV. 16). The further development of the spores has not 

 been observed in either ease. Both processes have been observed 

 in the same species, and it is suggested that there is an alternation 

 of sexual and asexual generations, the crystalligerous spores 



developing directly into adults, which in their turn produce in 

 their central capsules dimorphous swarm-spores (macrospores and 

 mierospores), which in a manner analagous to that observed in the 

 Volvocinean Flagellata copulate (permanently fuse) with one 

 another (the larger with the smaller) before proceeding to develop. 

 The adults resulting from this process would, it is suggested, pro- 

 duce in their turn crystalligerous swarm-spores. Unfortunately 

 we have no observations to support this hypothetical scheme of a 

 life-history. 



Fusion or conjugation of adult Radiolaria, whether preliminary 

 to swarm-spore-production or independently of it, has not been 

 observed this affording a distinction between them and Heliozoa, 

 and an agreement, though of a negative character, with the Reticu- 

 laria. 



Simple fission of the central capsule of adult individuals and 

 subsequently of the whole protoplasmic mass has been observed in 

 several instances, and is probably a general method of reproduction 

 in the group. 



The siliceous shells of the Radiolaria are found abundantly in 

 certain rocks. They furnish, together with Diatoms and Sponge- 

 spicules, the silica which has been segregated as flint in the Chalk 

 formation. They are present in quantity (as much as 10 per cent) 

 in the Atlantic ooze, and in the celebrated "Barbados earth" (a 

 Tertiary deposit) are the chief components. 



GRADE B. CORTICATA, Lankester, 1878(64). 



Characters. Protozoa in which the protoplasm of the cell-body, 

 in its adult condition, is permanently differentiated into two layers, 

 an outer denser cortical substance and an inner more fluid medul- 

 lary substance (not to be confused with the merely temporary 

 distinction of exoplasm and endoplasm sometimes noted in 

 Gymnomyxa, which is not structural but due to the gravitation and 

 self-attraction of the coarser granules often embedded in the 

 uniformly fluid protoplasm). 



Since the Corticata have developed from simple Gymnomyxa 

 exhibiting both amoeboid and flagellate phases of form and activity, 

 it results (1) that the forms of the body of many Corticata are 

 traceable to modifications of these primitive forms ; (2) that the 

 young stages of the Corticata are in the lower classes of that group 

 typical flagellulse or amoebulse ; and (3) that there are certain 

 archaic forms included in those lower classes whose position there 

 is doubtful, and which might be with almost equal propriety assigned 

 to the Gymnomyxa, since they are transitional from that lower grade 

 to the higher grade of Corticata. 



CLASS I. SPOROZOA, Leuckart (47); Syn. Gregarinida, Auct. 



Characters. Corticata parasitic in almost all classes and orders of 

 animals, imbibing nutriment from the diffusible albuminoids of 

 their hosts and therefore mouthless. In typical cases there is 

 hatched from a chlamydospore one or more modified nucleate or 

 non-nucleate flagellulse (falciform young, drepanidium phase). 

 The flagellula increases in size and differentiates cortical and 

 medullary substance. Fission is common in the younger stages of 

 growth. The movements now become neither vibratile nor amoe- 

 boid but definitely restrained, and are best described as "eugle- 

 noid" (cf. Flagellata, Fig. XX. 27, 28). The nucleus is single, 

 large, and spherical. No contractile vacuole and rarely any vacuole 

 is present. A size of yVth inch may be attained in this phase, 

 which may be definitely spoken of as the euglena phase corre- 

 sponding to the amoeba phase of Gymnomyxa. It is usually of 

 oblong form, with sac-like contractile wall of cortical substance, 

 but may be spherical (Coccidiidea) or even amoeboid (Myxosporidia). 



Conjugation, followed directly or after an interval by spornlation, 

 may now ensue. The conjugated individuals (two), or sometimes a 

 single individual, become encysted. The contents of the cysts now 

 rapidly divide (by a process the details of which are unknown) into 

 minute ovoid nucleated (?) bodies ; sometimes a portion of the 

 protoplasm is not converted into spores but may form sporodncts 

 (cf. capillitium of Mycetozoa). Each piece acquires a special 

 chitin-like colourless coat, and is then a chlamydospore. Rarely 

 one spore only is formed from the whole contents of a cyst The 

 spore-coat is usually thick, and remarkable for processes and other 

 accessory developments. The included protoplasm of the chlamydo- 

 spore frequently divides into several pieces before hatching. These 

 usually, when set free from the spore-coat, have the form of modified 

 nucleated flagellulse, i.e., flagellul* in which the protoplasm is not 

 drawn out into a thread-like flagellum but exhibits an elongate form, 

 uniformly endowed with vibratile activity. With few (if any) excep- 

 tions, the falciform young thus characterized penetrates a cell of some 

 tissue of its host and there undergoes the first stages of its growth 

 (hence called Cytozoa). In some forms the pre-cystic phase never 

 escapes from its cell host. In other cases it remains connected with 

 the hospitable cell long after it has by growth exceeded by many 

 hundred times the bulk of its quondam entertainer ; often it loses 

 all connexion with its cell host and is carried away to some other 

 part of the infested animal before completing its growth and 

 encysting. 



