462 MALL. [Vol. V. 



desired sections in no way distorted. On account of greater ease 

 in studying the sections, I cut the embryo at right angles to 

 the nape-breech length, at the same time striking the branchial 

 arches nearly at right angles. In all there were 351 perfect 

 sections, none lost, and only two or three slightly distorted. 

 The sections were enlarged 66| diameters, which at the same 

 time increased their thickness to 1 mm. Every second sec- 

 tion was now drawn on wax plates 2 mm. thick, and the 

 external outline of the section cut out. Before working the 

 interior of the enlarged sections, they were carefully piled, in 

 order to obtain the form of the exterior of the embryo. Next, 

 I made a plaster mould of the pile of plates, in order to keep 

 them in position. The plates were constantly kept within the 

 half-mould, in order to keep the model from becoming distorted. 

 This latter procedure proved of great value, as the plates were 

 cut into pieces in order to model the various organs. All the 

 wax representing the tissue between the organs and the exterior 

 of the body on the left side was removed, exposing the organs 

 as shown in the figure on Plate XXX. Then the organs were 

 freed from the opposite side, and the pieces of wax blended so 

 as to isolate each organ by itself. 



The body cavity was modelled as a corrosion preparation, by 

 drawing its outline on a second set of plates, and removing all 

 the wax representing the body cavity, then piling the plates again, 

 and finally casting the whole with Wood's metal. The metal 

 was next smoothed and imbedded in plaster of paris, from which 

 it was removed by boiling. The plaster mould was now cast 

 with solder, and the wax broken off. By this method a metal 

 cast of the whole ccelom was obtained. 1 



The shrinkage while imbedding in paraffin was slightly over 

 ten per cent, so our model, which represents the section of the 

 embryo enlarged 66f times, is but sixty times larger than the 

 specimen while in alcohol. All the measurements I give have 

 been reduced to correspond with those of the alcoholic specimen. 



1 Plates made of pure wax with a sheet of thin paper on either side, can be ob- 

 tained from Griibler of Leipsic. Plates of this sort can best be cut by means of a 

 jig-saw. I cast most of my plates by pouring the melted wax in a tank containing 

 hot water. The tank was of such a size that 500 grammes of wax made a plate two 

 millimetres thick. In most cases it is desirable to work with wax softened by adding 

 about five per cent of Burgundy pitch and about ten per cent of resin. 



