436 M. HASPER. 



clostermm forma mimtta. In other cases the egg-shells were put into 

 a larger jar fed with water from the tanks by means of a siphon. 



When the animals are in the stage required, they can be fixed in a 

 very simple manner. To the younger stages the fixing fluid was added 

 directly after having poured out the water. If the individuals were 

 further developed and were to be fixed with expanded polypides, they 

 were paralysed by some crystals of menthol floating upon the surface 

 of the water for some six hours and killed by a pipetteful of the 

 fixative, squirted out directly upon them in order to prevent them 

 from collapsing when the water was removed. As most of the fixa- 

 tives contain some percentages of acid more or less, the innermost 

 layer of the calcareous shell is dissolved and so the inner skin is spon- 

 taneously detached. When a mixture of a hundred parts of a saturated 

 solution of corrosive sublimate and five parts of glacial acetic acid was 

 used, the inner skin was lifted up by bubbles of carbonic acid in a few 

 minutes, so that it is easy to detach the membrane after having washed 

 the objects in the shells, and cut the latter into smaU pieces. The 

 pieces of membrane with the attached polypides are then treated in 

 the usual way. The membrane becomes very transparent in xylol or 

 cedarwood oil, and the object cannot be lost in the paraffin. The egg- 

 skin serves as a means of orienting the object too, and can be sectionised 

 so excellently that it is not in the slightest degree an impediment. 



I employed this method for the larvae of several species of Polyzoa 

 and a Tunicate of the family of Didemnidae. It is especially useful, 

 of course, when the larvae are of a dark colour, as, for instance, those 

 of Bugula neritina Oken ( = Cellularia neritina Pallas), which contrast 

 with the white ground most excellently. These larvae settle in 

 numbers just below the edge, or even on the free surface of the water 

 taking advantage of the surface-tension. 



