324 ORDER CHOANO-FLAGELLATA. 



The development of this interesting form, as reported by Haeckel, may be 

 thus summarized. The earliest or initial condition is represented by a single 

 spherical, egg-like body, containing a large central nucleus or endoplast and enclosed 

 nucleolus or endoplastule immersed within structureless transparent protoplasm, and 

 surrounded by a denser investing membrane, as shown at PI. I. Fig. 1 6 ; the nucleus 

 divides by fission into two equal halves, accompanied by a similar segmentation of 

 the circumjacent protoplasm, each section of which now envelops a single nucleus. 

 By a repetition of this process, similar to that of ordinary yolk-cleavage, four, eight, 

 sixteen, and finally thirty-two nucleated cleavage-spheres or daughter-cells are pro- 

 duced, and the segmentation is completed. The thirty-two bodies resulting from 

 this segmentation begin now to exhibit amoeboid movements within the investing 

 pellicle, and emit from their surface small, irregular pseudopodic processes ; these 

 gradually become longer and thinner, ultimately presenting the form of attenuate 

 vibratile flagella. United in a single spherical mass these bodies rotate slowly 

 within their membranous prison, which at length bursts asunder, leaving the com- 

 pound colony to swim away freely in the surrounding water, under the characteristic 

 adult aspect detailed in the foregoing diagnosis, and delineated at PI. I. Fig. 12. 

 Sooner or later this compound body falls to pieces, the individual zooids assume an 

 amoeboid form (Fig. 15), and it is believed become encysted and once more 

 repeat the cycle. During their active aggregated life the zooids ingest food 

 apparently at any part of their exposed anterior border, there being no distinct 

 oral aperture, and likewise during their amoeboid condition through any portion of 

 their periphery. 



Apart from the true affinities and significance of Magosph&ra previously dis- 

 cussed, the singular resemblance in general form, size, and plan of ciliation of the 

 separate zooids to the constituent elements of ciliated epithelium will at once 

 suggest itself to the practical physiologist. A coherent spherule of such epithelial 

 cells indeed, excepting for the absence of the contractile vesicles, would be in- 

 distinguishable from a colony-stock of Magosphara plamda, as originally described 

 and delineated by Professor Haeckel. 



Order V. CHOANO-FLAGELLATA, S. K. 



OR FLAGELLATA-DISCOSTOMATA. 



Animalcules exceedingly minute, highly polymorphic and variable in 

 form, usually exhibiting in their most normal and characteristic phase a 

 symmetrically ovate, pyriform, or clavate outline ; a single long, lash-like 

 flagellum produced from the centre of the anterior border, the base of which 

 is embraced by a delicate, hyaline, extensile and retractile, collar-like 

 expansion of the body-sarcode ; the collar in its extended condition infundi- 

 buliform or wineglass-shaped, when contracted subcylindrical or conical, 

 exhibiting in its expanded state a distinct circulating current or cyclosis 

 of its finely granular substance ; ingestive area discoidal, food-substances 

 being brought in contact with the expanded collar through the vibratory 

 action of the flagellum, first carried up the outside and then down the inside 

 of this structure with the circulating sarcode current, and finally received 

 into the substance of the body anywhere within the circular area circum- 

 scribed by its base ; faecal or waste products discharged at any point within 

 the same discoidal space ; a distinct spheroidal endoplast with a contained 

 endoplastule and two or more contractile vesicles usually conspicuous. 



