ON DEVELOPMENT ETC. OF PITORONTS. '*i^>^ 



Fig. ')8 c represents a portion of a transverse section throngli the 

 anterior region of the trunk of a larva belonging to type D. The 

 vessel in question here appears as a small canal {d.v.) running in 

 the stomach walls (x(.//i. and m..^Ji.). As will he seen in the figure, 

 the canal is distinctly lined with an epithelial cell-layer. The 

 dorsal vessel terminates anteriorly just 1)ehin<l the post oral seji- 

 tum, so that the whole course of the vessel is confined to the 

 trunk region. During larval life, the dorsal vessel does not extend 

 so far posteriorly as to l)ecome confluent with the cœcal con- 

 tractile capillaries which are formed at the point of juncture of 

 the stomach and the intestine. Thus we see in Fig. ö.j //, which 

 is taken from a transverse section through the lower portion of 

 the stomach, that the gut is covered with a thin mesohlastic widl 

 without a trace of the dorsal vessel, hut the capillaries {v.c.) are 

 here already developed at this period. In the above montioned 

 figure they are found as cell masses protruding into the trunk 

 cavity from the right side of the splanchnic attachment of the 

 ventral mesentery to the gut ; one capillary is seen in cross sec- 

 tion. The capillaries shown in that figure are certainly in an 

 early state of development, and, when fully developed, they appear 

 like a tuft consisting: of tolerablv loua;, blindlv ending tubes. 

 Sometimes I have observed that the capillaries are formed not 

 only on oue side of the ventral mesentery, but on both sides of it ; 

 and that they are not constantly formed on the gut walls, but 

 sometimes on the ventral mesentery. Thus we see in fig. 07 a on 

 the ventral mesentery {v.'//tes.) a rosette-like figure {v.c), the rudi- 

 ments of the capillaries seen under a low power. It is represented 

 highly magnified in fig. 07 c (taken from another neighbouring 

 section of the same series). Here are seen signs of cell-multipli- 

 cation on either side of the ventral mesentery (r./Ncs.), in places 



