DOTO. 



system ? The anus opens on the right side of the back, as stated above. Two delicate 

 vessels or ducts pass from the anterior portion of the stomach to the first pair of branchial 

 processes : the other branchial processes receive similar vessels from a central vessel which 

 passes from the posterior extremity of the stomach, and extends the whole length of the 

 body beneath the ovarium. The lateral vessels alternate a little, and are not always sym- 

 metrical : the last pair arise from the extreme posterior point of the central vessel. 



The hepatic glands are very highly organized, and almost fill the branchial processes, 

 with the exception of small passages hollowed out of the glandular mass, probably for the 

 circulation of the blood. There are no distinct sheaths as in Eolis, though we have observed 

 between the gland and the outer skin in B. coronata, a sort of network of fleshy columns 

 similar to what we have seen between the outer and inner sheaths of the papilla? of Eolis 

 papillosa. On placing one of the smaller branchial processes of B. fragilis in the com- 

 pressor of the microscope, the gland is discovered to be of a highly racemose character : 

 but for the complete understanding of its structure it is necessary to make a transverse 

 section of one of the larger processes, when the gland is perceived to be highly complicated 

 and delicately branched. The branches radiate from a minute central duct, and are much 

 divided and crowded with follicles : their extremities reach into the papilla?. The com- 

 pleteness of this organ as a secreting apparatus must be evident to physiologists, as well as 

 the improbability of its subserving any other function. 



Respiration is undoubtedly performed by the surface of the body as well as by the 

 branchial processes. Immediately beneath the skin of the body in B. coronata, is the same 

 network of fleshy columns observed in the branchial processes of that species ; and both in it 

 and in B. fragilis, the entire surface is covered with vigorous vibratile cilia. Cilia are also 

 on the branchial processes, but are most vigorous towards their bases. 



The heart is as completely organized as in any of the order : the ventricle is strong 

 and muscular, the auricle thin and membranous. 



The nervous system is furnished with four cerebral ganglions of nearly equal size, and 

 two small buccal ganglions of the usual form. The nerves are arranged much as in Eolis. 

 There appear to be about ten principal pairs, and a few smaller ones, which we were unable 

 to trace. The olfactory ganglions are at some distance from the cerebral ganglions to which 

 they are united by large nerves : they are round, and placed at the bases of the tentacles. 

 The eyes are also placed a little way from the cerebral ganglions, and are very small. The 

 otolites of the auditory capsule are numerous and elliptical. 



The generative organs do not materially vary from those of Eolis. The ovarium, how- 

 ever, is above the great central vessel of the digestive system. 



EXPLANATION OF THE PLATE. 



Eig. 1. General view of the viscera of Doto fragilis, seen from above :~a, buccal mass; b, 

 oesophagus j c, stomach; d, intestine; e, anal nipple;/, salivary gland; g, accessory 

 salivary gland ; h, h, h, h, lateral vessels or ducts leading from the branchial glands to 

 the central vessel connected with the stomach; i, ventricle of the heart; j, auricle of 

 the same; k, k, k, generative organs; /, cerebral ganglions; m, m, olfactory ganglions. 

 I. the digestive apparatus exposed :— a, buccal mass; h, oesophagus; c, stomach; d, intes- 

 tine ; e, anus ; /, f, great central duct ; g, g, g, g, lateral ducts from the branchial 

 glands ; h, salivary gland ; i, accessory salivary gland. 



