ORGANS OF SECRETION. 577 



their alimentary canal, and the only distinct follicles per- 

 ceptible in their body, may be considered as analogous to 

 the hepatic coeca developed from the sides of the intestine, of 

 long gastric cavity, of annelides. The hepatic follicles in most 

 of the lower invertebrata, and in the first stages of their de- 

 velopment in the highest vertebrated animals, admit the 

 contents of the intestine into their interior, as well as in 

 polygastrica. Were the secretions furnished by the interior 

 lining of these follicles in the polygastrica, different in their 

 characters towards the anterior and posterior ends of the 

 digestive canal, the follicles nearest to the masticating organs, 

 might be considered as salivary, and those nearest to the 

 anus, as urinary glands, as in many articulata, but these 

 differences and analogies are not established in this class. 

 A larger single or double follicle, more various in form 

 and colour, than the intestinal, and the small contractile 

 follicle, seen in most polygastrica, have been imagined to be 

 connected with the generative system, and the former to 

 represent a testicle, and the latter a vesicula seminalis, but 

 with as little evidence of such analogy. As the whole inter- 

 nal cavity of polygastrica, whether a canal as in the diaccelous 

 and cyclocoelous forms, or a mere concavity as in the anen- 

 terous species, is most analogous to the gastric sac of higher 

 animals ; so are all its follicles most analogous to hepatic or 

 biliary tubuli, forming the simple condition of the liver in 

 these animals. Some polygastrica, as peridinium, synchseta, 

 prorocentrum, illuminate the seas where they occur, but 

 the source of their luminous secretion, is as little known as 

 that of many higher animals. The flesh of poriphera forms 

 a universal blastema for all the glands and other organs or 

 higher animals, but in which none are yet developed ; and if 

 its constituent granules enjoy an independent existence, like 

 the individuals of aggregate animalcules, they probably 

 exhibit also in their interior, the hepatic follicles, or so- 

 named stomachs of all other known polygastrica. Fine 

 pellicles of mucus or epithelium are secreted by the sides 

 of the internal canals of poriphera, and are constantly thrown 

 out, along with the respiratory currents, from the numerous 

 large vents of their surface. 



From the fleshy surface of lobularia, and other polypiphera, 

 thin mucous pellicles are periodically formed and detached, 



PART VI. P P 



