1 82 BRACE. [Vol. XVII. 



sections of the ventral side show that they are not pits at all, 

 but the terminations of deep ciliated grooves which curve for- 

 ward and outward from the mouth to the edge of the pro- 

 stomium (PI. XXI, Fig. 13). 



The mouth is circular, bordered posteriorly and laterally with 

 a thick swollen lip, which may be greatly extended, and which 

 is continued as the posterior wall of the ciliated furrows. The 

 cilia of the grooves, and those around the mouth, are excep- 

 tionally long. Sense organs are as numerous along either 

 side of the furrows as on the prostomium. 



Vejdovsky describes a nerve connecting the lateral pits with 

 the brain. I find muscle fibers here, but no nerve, and from 

 the nature of the structure should not expect to find one. 



Sense Organs. — There are many large pear-shaped cells, 

 that have the appearance of sensory cells, lying in all parts 

 of the prostomium and disposed through the body segments 

 (PI. XXI, Fig. 14). The cytoplasm of these cells is finely gran- 

 ular and deep-staining, the nucleus is of medium size, coarsely 

 granular, and usually eccentric, taking its position at the base 

 of the cell. Between the nucleus and the opposite end of the 

 cell there is a large, sharply outlined, clear space containing 

 a refractive body with peculiar granulations at its periphery 

 (Fig. 14) which may represent an otolith. These cells are 

 sometimes isolated, but are often collected into small groups 

 (Fig. 15), as seen to best advantage in the prostomium. They 

 suggest sense organs of some kind. They have no pigment. 



At the anterior end of the prostomium there is a group of 

 about fifteen of these large compound organs, crowded together 

 so closely that their sides are somewhat flattened against each 

 other (Fig. 16). Back of these there are smaller compound 

 sense organs, some distance apart, arranged in rows across the 

 ventral surface of the prostomium, and there are large sense 

 organs along both sides of the ciliated furrows leading to the 

 mouth (Fig. 16). The smaller compound sense organs are 

 also found on the ventral side of the segments back of the 

 mouth. All of these sense organs lie immediately under the 

 epidermis, so that they project slightly into the body cavity. 



Aeolosoma undoubtedly possesses the essential annelidan 



