DAVENPORT: PROCESSES CONCERNED IN ONTOGENY. DN 
of Turbellaria according to lijima (Zeitschr. f. wiss. Zool, XL. 455). 
Among Vertebrates, we have the observations of Paterson, (Figure 3,) 
according to which the sympatbetic nerve arises by the aggregation of 
mesenchymatous elements into a strand; of His, who affirms the origin. 
of the spinal and the olfactory ganglia from migrating cells; and of 
various authors, who make blood capillaries and lymph vessels arise by 
this process (cf. M., pp. 217, 413). 
Carotia 
Ay te ry. 
b. Next we must consider the aggregation of mesenchyme into a 
superficially extended body,—the formation of a layer. This process 
does not seem to be very common ; one example is seen in Figure 4. 
c. As the last of these processes of aggregation we have the case of 
aggregation into a mass. This wide-spread ontogenetic process may be 
illustrated by the formation of gemmules in a marine sponge (Figuro 5). 
Other examples are found in the formation of the adductor muscles of 
Fig. 3. Cross section of a rat embryo in the upper thoracie region, showing the 
development of the sympathetie nerve (between spinal nerve and carotid artery). 
From A. M. Paterson, ’91, Trans. Roy. Soc. Lond., Pl. XXII, Fig. 4. 
Fig.4. Later stage of the embryo shown in Figure 1. The migrating proto- 
plasm has aggregated itself into a layer at the surface of the embryo. See K. & H., 
Fig. 449. 
Fig. 5. Section of a marine sponge (Esperella), showing a gemmule, a mass of 
aggregated mesenchyme which is about to produce a gemmule (1%), and migrating, 
not yet aggregated mesenchyme (1). After H. V. Wilson (04, Jour. of Morph., IX. 
DU XLV 
