OUTGROWTH OF THE NERVE FIBER 
805 
thus served to confirm the conclusions which have been drawn from 
the study of the former. On the other hand, the experiments have 
been controlled by observing the behavior of other embryonic 
tissues, such as muscle plates, ectoderm from the abdominal region, 
notochord, and yolk endoderm, under the same conditions. The 
results have shown, that while all tissues have certain features 
in common, each has nevertheless its specific activities, and these 
peculiarities coincide, as far as they go, with the activities shown 
by the respective tissues in the normal embryo. In other experi- 
ments separate pieces of ectoderm or muscle plates were placed 
in the lymph close to the nervous tissue, with a view to testing 
the power of the former tissues to influence the growth of nerve 
fibers. For instance in some experiments the medullary cord of 
the trunk was divided into its dorsal and ventral portions, and 
each was implanted separately with pieces of epidermis or of myo- 
tome, in the hope that it might be possible to show in this way 
that each of these tissues exerted some characteristic influence 
upon particular kinds of nerve fibers, the epidermis upon the 
sensory and the muscle tissue upon the motor. The results of the 
latter experiments were entirely negative ; but since they were few 
in number and since the conditions of experimentation were not 
ideal, hope that this method may ultimately yield important dis- 
coveries need not necessarily be abandoned. 
The total number of preparations made was 211. Permanent 
records have been kept for 150 of these, the remaining ones having 
given no promise from the beginning. Of the 150 cases, 35 have 
been rejected because they were found to be in bad condition before 
they could be expected to yield positive results. Table 1 shows 
how the experiments were distributed amongst the various em- 
bryonic tissues. 
The specimens were studied almost exclusively under the w^ater 
immersion lens, D* of Zeiss. In fact this lens is almost indis- 
pensable for the wwk. It has such a long working distance that 
the depths of the preparation can be readily examined without 
fear of breaking the cover. The magnification obtainable by the 
combination of this objective with eye-piece No. 4 is about 400 
diameters, which is sufficient for all practical purposes. It w^as 
