338 DESCRIPTIONS OF PREPARATIONS. 



' Root-cells,' like the Ooecia, are regarded by Vigelius as organs, not as modified 

 zooecia (Bijdrag tot de Dierkunde, xi. 1884). They are, however, often jointed 

 and branched, and may serve as connecting links between adjoining branches in a 

 colony. See Busk's article on Kinetoskias, Q. J. M. xxi. 1881. 



The Avicularium, Vibraculum, and Stem-cell, together with the Ooecium and 

 Radicle-fibre according to some authorities, are zooids modified from the ordinary 

 structure to discharge certain special functions. Modifications of this character 

 constitute Polymorphism. They must be carefully distinguished from modifications 

 of outward form not accompanied by a specialised function, such as are found in 

 many Calcispongiae, and have been termed by Haeckel Polymorphosis. 



When only two organisms or three, differ by way of polymorphism, the terms 

 Dimorphism or Trimorphism are sometimes used. Instances are not uncommon in 

 the animal kingdom. There can be no doubt that the Medusa and Hydroid polype 

 are dimorphic forms, and there are other modifications of the hydroid, such as the 

 Blastostyle, the Dactylozooid, the Snake-like zooid of Ophiodes^ &c. The worker bee 

 is a dimorphic female ; the soldiers and workers among the Termites are trimorphic 

 with the fully-formed male and female. 



The phrase sexual dimorphism is used to denote the differences other than the 

 usual anatomical characters which separate the two sexes. Such differences are ex- 

 ceedingly common, and are sometimes carried to an extreme ; e. g. among Lepidoptera 

 species or genera have been based on characters which are really only distinctive 

 of sex. And in the Insectan order named the individuals of broods appearing at 

 different times of the year often differ from one another in a marked manner. In 

 this case the phrase seasonal dimorphism is employed. 



Polyzoa, Ray Lankester, Encyclopaedia Britannica (ed. ix), xix. British 

 Marine Polyzoa, Hincks, 2 vols. London, 1880. British Fresh-water Polyzoa, 

 Allman (Ray Society), 1856; cf. Hyatt, Proc. Essex Institute (U.S.), iv. 1865; cf. 

 Allman, decent progress of kncnvledge of Fresh-water Polyzoa, J. L. S. xiv. 1879; 

 of Marine Polyzoa, ibid. xv. 1881. Vigelius, Bijdrag tot de Dierkunde, xi. 1884 

 (not seen). 



Membranipora (= Flustra) membranacea, Nitsche, Z. W. Z. xxi. 1870-1871. 

 Flustra membranaceo-truncata, Vigelius, Biol. Centralbl. iii. 1883-84, and Id. 

 Bijdrag tot de Dierkunde, xi. 1884. Kinetoskias, Busk, Q. J. M. xxi. 1881. Hypo- 

 phorella, Ehlers, Abhandl. k. Gesellsch. der Wissenschaften. Gottingen, xxi. 1876 

 (not seen). Halodactylus diaphanus, Kohlwey (Inaug. diss.), Halle, 1882. Alcyo- 

 nellafungosa (freshwater), Nitsche, Archiv fiir Anat. Physiol. 1868. 



Avicularium and Vibraculum. Hincks, Introduction to 'Marine Polyzoa' 

 (supra]. Relation of two. Id. A. N. H. (5) ix. 1882. Movements of Vibracula in 

 Caberea. Id. Q. J. M. xviii. 1878. 



Endosarc, &c. Joliet, Bryozoaires d. Cotes de France, A. Z. Expt. vi. 1877. 



Formation of generative products in Cheilostomata. Vigelius, Biol. Centralbl. ii. 

 1882-83. 



Ooecium. Vigelius on Flustra membranaceo-truncata (supra] Nitsche, Z. W. Z. 

 xx. 1870 ; Hincks, xiii. 1873, p. 30. 



Budding in Polyzoa. Haddon, Q. J. M. xxiii. 1883. 



Discussion of Affinities. Harmer on Loxosoma, Q. J. M. xxv. 1885, p. 304 et 

 seqq. 



