134 LECTURE VII. 



spermatic force in the ordinary form of spermatozoa seem to be the 

 last act of the free medusoid individuals which are liberated from the 

 Coryne, Syncoryne, and certain species of Campanularia and Tabu- 

 laria; and the hydriform polype which results from the development 

 of such ovum, together with the organically connected colony of 

 such, developed by successive gemmation, and bearing the name of 

 Coryne, Campanularia, &c., are larval forms, procreating partheno- 

 genetically, and answer to the larval vesicles developing the cer- 

 carioids which ultimately change into the generative forms of tre- 

 matode entozoa. With regard to those numerous species of Sertularia 

 (e. g. *S'. Polyzonias, ahietina, rosacea, pumila, Jialecina, Beanii, 

 uher, Dal., argentea, aniennina, ramosa, thiiia) and of Plumularia 

 (e. g. PL falcata*, pinnata), in which the ovicapsules give issue to 

 planulaes, subsequently transformed into sertularian polypes, their 

 genetic cycle is of a more simple character ; the germinal basis of 

 the planula must be viewed as an ovum impregnated by the 

 spermatozoon developed in the sperm-capsules of the males above 

 described. 



The Antliozoa {Jrgs. 63-67.), or polypes of the second great class, 

 characterised by a distinct abdominal cavity in which their simple di- 

 gestive sac is suspended, constitute the most numerous and important 

 part of the whole race, and include the largest individuals. They 

 are principally the inhabitants of the warmer or tropical seas. 



They are subdivided chiefly according to the number and structure 

 of their oral tentacula. Most of the species have only eight of these 

 radiated prehensile organs : the rest have a greater number. To this 

 latter group belong the soft-bodied and solitary species called Sea- 

 Anemonies, or Actinice, which are common upon our own coasts. 



In the Actinia here dissected (^Jig. 63.), you will see that the skin 

 of the body, a, is thick and opaque : in the living Actinia, it is lubri- 

 cated by a mucous secretion : it is lined by a thick stratum of mus- 

 cular fibres, the disposition of which is indicated by the superficial 

 striae, and may be shown, in the larger Actiniae, to be in antagonising 

 longitudinal, and transverse or circular, fasciculi. In the middle of 

 the circle of the tentacles, c,c, is situated the contractile and dilatable 

 mouth, d, fi'om which a short oesophagus leads to a large gastric 

 cavity, e, the parietes of which are connected by a great number 

 of membranous vertical folds, g, g, with the external wall of the body. 

 The tentacula are beset with numerous dart-cells : they are tubular, 



* The ciliated character of the embryo, and its locomotive power, settlement and 

 metamorphosis into the Plwnuhtria wore first discovered, and are hcantifiilly de- 

 scribed by Ur. Grant, in CXI*., who calls tlie embryo " ovum." 



