OF THE PHYTOZOA. 145 



which they arc imbedded, he called the lorica, and stated that propagation 

 occurred by self-di\'ision within the envelope, and probably also by ova. 



The genera Chlamydomonas and Gyges, or Cldamydococcus (XIX. 9-31), 

 offer an exception to the other members of the family in not producing 

 aggregate forms or colonies, at least not in their assumed typical phase. 



A\Tiilst denying in toto the elaborate animal organization presumed by 

 Ehrenberg, M. Dujardin nevertheless continued to recognize the Volvocina 

 as animal structures, and contented himself with merely proposing a dif- 

 ferent distribution of the genera. However, since this distinguished French 

 naturalist wrote, the opinion has been powerfully advocated, and everywhere 

 gaining ground, that the Volvociaece belong to the vegetable kingdom ; con- 

 sequently their structiu'e and \dtal phenomena receive quite a different inter- 

 pretation from that given by the writers above named. 



The Vohocineoi are now, in the language of algologists, ' Tetraspora,'' of 

 the family Palmelhce or PalmeUacece. The monadiform beings are ' primor- 

 dial cells,' and, in more general language, ' corpuscles,' whilst the common 

 pellicle or nidus connecting them is called by Cohn and others the ' envelope- 

 cell.' The author just named says {Enhv. p. 165), that, from his observa- 

 tions on Cldamydococcus, Chlamydomonas, and Stephanosphcpra, the Volvo- 

 cinece in general consist essentially of two parts : — 1. of a colourless, hyaline, 

 completely closed, and usually spherical envelope-cell composed of cellulose ; 

 and 2. of green 2)rimordial cells, single in the two first-named genera, but 

 eight in number in Steplianosphoira, enclosed within the envelope -cell. In 

 each case these cells are simply primordial sacs, unenclosed by any special 

 firm cellulose membrane, and consist of a fine granular protoplasm, coloiu'ed 

 green or red by clilorophyll, or by a peculiar oil (XIX. 48, 49). The proto- 

 plasm forms only the outer layer of the ceUs, and is often prolonged on the 

 inner siu-face of the ' envelope-cell ' in the form of delicate mucous fibres 

 (XIX. 53). The primordial cells are moreover themselves elongated from 

 before backwards, forming a colourless apex from which two vibratile fila- 

 ments take their rise, and passing through two foramina in the envelope- 

 cell, stretch themselves outwards in the siuTounding water, and by their 

 vibration serve to move the entire compound organism. The only difference 

 between ChJamydococcus and Stephayiosplicera is one affecting the mode of 

 development, in which only the primordial cells (not in any way the common 

 envelope) take part. These cells divide first into two, then into four, then 

 into eight or more daughter- cells (macrogonidia) (XIX. 40, 41, 42) ; but 

 after the third or the second, and often, indeed, after the first act of division, 

 a permanent generation results. Thus, in Chlamydomonas and Chlamydo- 

 coccus, each of the daughter- cells becomes free and independent, encloses 

 itself within an envelope-cell of its own, and after developing two fibres, 

 breaks through, mth their aid, the common envelope of the parent-cell (XIX. 

 23-26 and 30). In Stephanospha=ra, on the contrary, the eight primordial 

 cells produced hj the third act of fission secrete around themselves a common 

 envelope (XIX. c>Q), which invests them like an integument, first Ipng close 

 upon them, but afterwards, through the imbibition of water, raised from 

 them all round, assuming a globular fonn ; but so that the primordial cells 

 occupy the periphery at the equator of the globe like a ring or zone (XIX, 

 57, 58), having their eight pairs of filaments protruded through the openings 

 in the common envelope (XIX. 38). ChJamydococcus and Chlamydomonas 

 stand in the same relation to Stephanosphcera that Pleurococcus does to Pal- 

 mell-a, Phycastnim to Desmidium, Navicula to Schizonema, VorticeVa to Epi- 

 stylis, or as Hydra to Campanularia. 



But, further, a second mode of development, \^z. by microgonidia, prevails 



