364 OILMAN A. DEEW. 



correspond very closely to mucus, and they are generally 

 referred to as mucus glands. During the greater part of 

 the year the hypobranchial glands of both sexes of Nucula 

 delphinodouta are rather small and inconspicuous. They 

 contain rounded or oblong masses of a refractive material 

 that takes no stain. The cells themselves are small, and do 

 not seem to be secreting actively. The hypobranchial 

 glands of specimens of males seem to have the appearance 

 that has been described, no matter what time of the year 

 they are collected. As the breeding season approaches, the 

 hypobranchial glands of the females become greatly dis- 

 tended with secretions. The rounded or oblong masses that 

 ai"e common at other seasons of the year are now seldom 

 found, and the cells are packed full of rather large granules. 

 Immediately after the brood-sac is formed, the cells of the 

 hypobranchial glands appear shrunken and free froui 

 granules, and the glands have the appearance of having 

 discharged their secretions. After examining a large number 

 of specimens, I have become convinced that the hypobranchial 

 glands furnish nearly all of the material from which the 

 brood- sacs are formed. Specimens kept in aquaria do not 

 form brood-sacs, and accordingly the processes of their 

 formation have not been observed, but it seems probable that 

 the secretions from the glands are passed posteriorly by cilia 

 on the mantle, and probably swelled out into a bubble by 

 the respiratory current of water. While the material is still 

 soft it adheres to the foreign bodies with which it comes in 

 contact. 



Well-developed hypobranchial glands are present in only 

 a limited number of Lamellibranchs, and their special func- 

 tion is hard to determine. It is interesting to find that they 

 are concerned in the formation of the brood-sacs in this 

 species, but this is the first instance that has been reported 

 where such a sac is formed. It may be that other forms 

 that possess especially large hypobranchial glands will be 

 found to form similar brood-sacs, but this will not hold true 

 for all. Nncula proxima has rather large hypobranchial 



