ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 741 



tentacles. The lophophore varies in shape in different species, and the 

 tentacles vary in length. Each tentacle has an epidermis consisting 

 of a single row of cells over the greater part of the surface, hut on 

 the inner surface it is two or three cells deep, and those of the 

 outer layer here carry long cilia. Within the eiiidermis is a ring of 

 tissue which forms the skeleton ; this encloses a spacious cavity, which 

 is continuous helow with the ccelom. A nerve passes up each tentacle 

 on its inner side. The tentacles are not united by a true membrane, as, 

 for instance, in Plumatella, but are merely connected together by the 

 trabecula3 of basement-tissue. 



The i)it at the base of the inner series of tentacles does not seem, as 

 some authors have thought, to be sensory, but rather glandular. The 

 epistome has not the appearance figured by Allman, whose representa- 

 tion conveys quite a wrong idea. Its dorsal surface is covered by a 

 cubical epithelium, continuous with and similar to the surrounding 

 epidermis ; its oral surface agrees with the epithelium of the oesophagus, 

 and consists of very elongated, narrow, columnar cells carrying cilia. 

 At the base of these is seen nervous tissue. 



The nervous system lies immediately below the epidermis ; between 

 the basement tissue and the epidermis there is a narrow layer of granular 

 substance, which is not stained in borax-carmine ; in this layer there are 

 a few rounded nuclei belonging to small nerve-cells, and numerous 

 delicate fibres crossing tbe gi'anular substance from the overlying 

 epidermal cells. This is the nerve-band; it follows the lophophore, 

 passing all round the oral side of the animal, and curves round at the 

 sides of the nephridial ridges, following the spiral course of the lopho- 

 phore. From this band a nerve goes to each tentacle and nephridium. 

 There is no concentration to form a ganglion anywhere. Afler giving 

 some further details, the author describes the digestive system. The 

 coelom is divided into two very unequal cavities by a septum, the histo- 

 logical structure of which is of some interest. It consists of a nearly 

 homogeneous dense matrix, sometimes fibrous, in which are imbedded 

 small spindle-shaped cells with rounded nuclei. Here and there are 

 larger and smaller spaces, lined by cells, which appear to place the 

 supraseptal in communication with the infraseptal cavity. 



After some observations on the vascular system, nephridia, and 

 gonads, the author enumerates and defines the known species of Phoronis, 

 and then passes to consider the relations of the genus to other animals. 

 So far as the Brachiopoda are concerned, resemblances are certainly to 

 be seen in the arrangement of the tentacles and the division of the 

 coelom into a visceral and a tentacular cavity, but detailed comparison 

 of adults, of larvae, of the modes of development, shows that there is no 

 close relation between Phoronis and the Brachiopods. At first sight 

 Phoronis has a great resemblance to the Polyzoa, but the differences in 

 structure are very considerable. Thus Phoronis has a closed vascular 

 system, and the Polyzoa have none ; the Polyzoa have a suboesophageal 

 ganglion, while the nervous system of Phoronis is in an embryonic 

 condition. The gonads of Phoronis are unpaired, of the Polyzoa paired, 

 and the mode of origin of the mesoblast is very different in the two groups. 

 On the whole, this difficult form seems to stand nearest to the Sipunculids, 

 especially in the developmental history, where there are many, some 

 important, points of similarity. The ai'rangement of the alimentary canal 

 is the same in both, and it has the dorsal flexure found in the trochosphere. 



