322 ROY L. MOODIE 
‘“‘the first formation of bone in relation to the sensory organs 
of the skin,”’ although the problem has been touched by a num- 
ber of investigators, notably Schleip (04), who discussed the 
origin from the ectoderm of the osteoblasts forming the bones 
surrounding the latero-sensory canals, thus indicating a double 
origin for the bones of the head. Schleip does not, however, 
entirely agree with Klaatsch (95) regarding the origin of the 
osteoblasts from the ectoderm, maintaining that from the crowd- 
ing of the cells it is difficult to determine their origin. Concern- 
ing the influence of the latero-sensory canals in stimulating 
the ‘skeroblasts’ to activity, Schleip has little to say, but 
Klaatsch’s work shows that for the peripheral bones the lateral- 
line system does have an influence. The classic papers of Mc- 
Murrich (’84) and Wright (84) were also studied and were 
found to be of great value, as attested by the references in the 
following pages. 
MATERIAL 
The problem was first attacked on fresh living material at 
Woods Hole. Here the embryos and larvae of various species 
of fishes were studied under the polariscope, which had previously 
been found useful by other investigators in determining the growth 
of the skeleton in echinoderm larvae. Vertebrate material, how- 
ever, studied in this manner proved very unsatisfactory. 
Pigment was the chief cause of confusion and the density of the 
tissues was another. Spicules of bones are occasionally evident 
and their relation to the canals can be seen, but in a very unsatis- 
factory manner. 
After some deliberation it was decided to undertake the study 
of the problem in the young Amiurus. While the work was in 
progress, great aid was rendered by the appearance of the ex- 
cellent study of Kindred’s (19) dealing with the development 
of the skull of this genus. The first step in the undertaking was 
to determine at what age the skull bones began to develop. This 
was done by clearing in KOH,? according to the Schultze method, 
2 This method has been elaborated by Mall, Am. Jour. Anat., vol. 5, pp. 433-— 
458, 1906, and by the writer in the same journal, vol. 7, p. 433, 1908.’ The chief 
advantage of the method is that one is enabled to determine the earliest appear- 
ance of the spicules of bone which are often overlooked in histological sections. 
