MUSEUM OF COMPARATIVE ZOOLOGY. 171 



Thus we find that, of the authors cited, Bobretzky, BiitschH, and 

 — as far at least as regards the aquatic pulmonates — Fol consider the 

 central nervous system as originating from the mesoderm. Rabl is a 

 little doubtful as to its mesodermic origin in Bythinia. Rabl, Fol, and 

 Salensky are the only investigators who consider any portion of the cen- 

 tral nervous system as arising by invagination, and then only in certain 

 Gastropods.^ 



The following observations were made upon embryos of Limax maxi- 

 nius obtained from adults kept in captivity. Under favorable circum- 

 stances, they lay abundantly during the latter part of September, and 

 through October and November. After numerous trials, the best method 

 found was to keep about twenty-five or thirty in a large tin pail, the 

 cover being perforated with small holes. Instead of using moss to se- 

 cure the necessary moisture, the slugs were fed upon lettuce or cabbage ; 

 the latter is the better of the two. This food affords at the same time 

 sufficient protection against desiccation, a suitable retreat for the slugs, 

 and a place where they may lay the eggs. It should be changed every 

 other day, — every day if the weather is warm, — and the pail should be 

 washed thoroughly each time. One of the advantages of using a tin 

 vessel is the ease with which it may be kept clean. Cabbage will keep 

 longer than lettuce, and the slugs lay more abundantly when fed upon 

 it. The eggs were generally found in the morning, sometimes at night, 

 in bunches of from thirty to forty. They are more abundant at first 

 than after the slugs have been kept some time in confinement ; it is 

 therefore better to obtain at intervals fresh supplies of small numbers 

 of slugs than to procure a larger number at one time. As soon as 

 found, the eggs were removed to a watch-glass containing water ; this 

 was placed in a tumbler already about half filled with moss or moistened 

 paper, having a perforated tin cover. The eggs must not be allowed 

 to become dry. For a few days they should be carefully examined under 

 a microscope, every twenty-four hours or oftener, and all those which fail 

 to develop should be removed at once. In the course of a few days these 

 can be readily detected with the naked eye by reason of the greater 

 opacity of the eggs, and the presence of a whitish spot in them due to 

 the disintegration of the embryo. 



^ The brothers Sarasin, in hiter researches in Ceylon ('87, pp. 59-69) on a spe- 

 cies of very large Helix, find that there are two invaginations of the ectoderm on 

 each side of the head to form the cerebral ganglia, and Kowalesky ('83*) had found 

 several years before that there were in Dentalium two deep invaginations, one on 

 each side. 



