6 ■ Hjalmar Théel, 



the stages in which they are figured on the last plates of this report, 

 towards the end of August. 



As to the small »humid chambers», which are to be placed on 

 the microscope-stage, and which have long been in use for the pur- 

 pose of studying the different phases in the development of the eggs, I 

 availed myself of two kinds, one with the water-drop hanging down 

 from the under surface of the cover-glass, the other with the water-drop 

 slightly pressed between the object-glass and the cover-glass. Of these 

 two kinds of microscope-aquaria I prefer the latter, because the water- 

 drop does not shake or tremble so much, for which reason one need 

 not fear that the egg living in it will get disturbed so easily. To pre- 

 vent the compression of the eggs, it is as well to place between the 

 glasses some small particles of wax, and in order to hinder the evapo- 

 ration of the water, to tighten and fix the cover-glass with melted pa- 

 raffine or wax. In such chambers I have succeeded in following the 

 gradual changes in the development of the same egg for several days, 

 from the impregnation to the first Pluteus stage. Meanwhile the micro- 

 scope-aquaria should be kept in a moderate temperature. 



Lastly, I may refer in a few words to my practical acquaintance 

 with the process of fertilization of the eggs of Echinocyamus. There 

 is no difficulty at all in artificially fertilizing eggs of this animal, but 

 in order to be successful it seems to be of a certain importance to 

 choose animals accustomed to live under almost the same conditions. 

 The specimens of Echinocyamus which I generally used for my experi- 

 ments, lived at a depth of a few fathoms on a clay bottom close to 

 Fiskebäckskil, a sea-side place at the west-coast of Sweden. The tem- 

 perature of the water is during the summer-time rather high and the 

 clay at the bottom is mixed with the refuse animal and vegetable matter 

 from the kitchen of the Baths Restaurant, which possibly explains the fact 

 that the Echinocyamus occurs there in very great numbers, while it is much 

 rarer in cleaner and colder water. If I placed the eggs of a female 

 individual, taken from this locality, in the male fluid from another indi- 

 vidual dredged in the open sea from a greater depth, where the water 

 is much cleaner and colder, my experiments were unsuccessful and the 

 larvœ were abnormal. If this proves to be a rule, and not a mere acci- 

 dent, it is probably due to the different modes of life of the two indivi- 

 duals in question, which result in such a remarkable diff'erentiation that 

 the normal evolution becomes impossible. However, the experiments 

 ought to be repeated, in order to throw light upon this matter. 



