394 DR W. CARMICHAEL M'INTOSH ON THE STRUCTURE OF THE 



stages, remove all doubt on this subject, and show that these globular bodies 

 belong neither to the nervous nor the circulatory system. The funnel-shaped 

 duct (m!) is richly ciliated, and the cilia may be traced to the sac, wherein they 

 are continued as a linear streak along its exterior border, but its general mass is 

 not ciliated. The ciliated curve along the external border is well seen in young 

 specimens, but the exact superficial extent of the ciliation is difficult to deter- 

 mine. In favourable examples the walls are observed to be furnished with finely 

 granular cells, which have a clear and distinct nucleus. These cells are most 

 evident on the inner and posterior curves, the outer curve being pale. The sacs 

 project posteriorly into two large cavities (Plate XI. fig. 1, .?, s) on each side of the 

 proboscidian tunnel, and are thus laved by the circulating fluid, which rushes 

 forwards from the walls of the digestive cavity ; but there is nothing to support 

 M. Van Beneden's views* as to their continuity with the circulatory system. 

 Their relations to the ganglia have been adverted to previously, and are well 

 shown in some horizontal sections, where one sac has been severed considerably 

 lower than the other. Just in front of the external border of the curved dorsal 

 groove on the snout of Meckelia annulata is an ovoid body apparently homolo- 

 gous with the foregoing ; but I have not yet been able to trace its anatomy, on 

 account of the opacity of the cutaneous tissues in this animal. 



The functions of these bodies would seem to be excretory. Their gradual 

 advance in position and proportional diminution in size in the developing animal 

 would seem to indicate that their function is more important in the young than 

 in the adult. They are quite absent in Cephalothrix. 



Prof. Keferstetn does not enter into structural detail with regard to these 

 organs in this group, but states they lie at the posterior end of the lateral 

 fissures. 



Eyes.— These are simply masses of black pigment, arranged on the sides of 

 the snout with greater or less regularity, and without any special optical struc- 

 ture. The textures of the head and nerve-fibres themselves are so unfavourable 

 for observation that I have had difficulty in making out nerve-branches thereto. 

 A more definite structure is observed in the Ommatopleans, both as regards 

 nervous elements and complexity of organisation. Some Borlasians have no 

 eyes (a remark, however, which does not apply to Lineus longissimus), or have 

 them only temporarily in their young state, like the developing oysters and 

 Terebratulse ; while all the Ommatopleans possess them. It is a curious fact 

 that in transverse sections of the snout (such as Plate X. fig. 4) considerable 

 pigment-specks are seen towards the ventral surface. 



* Op. eit. p. 12. — " En avant, ces vaisseaux aboutissent au-dessous des ganglions cerebraux, et, 

 si nous ne nous trorapons, ils se renflent la en vesicules qui semblent appartenir aux ganglions memes, 

 et qui conduisent leur contenu a l'exterieur par un court canal excreteur aboutissant au fond de la 

 fossette laterale." 



