ON AMPHIIJNA PAKAGONOPORA 75 



found what are undoubtedly the earhest stages of growth of 

 these masses, and several other facts of interest. 



The earliest certain developmental stage of the amorphous 

 mass which I have observed was approximately spherical and 

 measured 29 microns in diameter (PL 5, fig. 40, x500). Tho 

 mass simply consists of a globule of plasm with a dozen or so 

 nuclei embedded in it, and is surrounded by a relatively thick 

 capsule of loose concentrically arranged fibres ; usually 

 capillaries are to be seen near by. I have seen about a dozen 

 of these early stages ^ (one measuring 40-2 microns in diameter 

 is shown in PI. 5, fig. 41, x500, and another larger one in 

 PI. 5, tig. 42, x500). It will be noticed that these minute 

 masses are smaller than the larvae liberated from the uterus 

 of the worm, and it is therefore evident that the larva must 

 undergo some process of subdivision, probably in an inter- 

 mediate host, before infection of another fish can occur. I have 

 not been able to trace these masses back to a unicellular stage. 

 Encapsulated masses larger than these early stages are very 

 numerous, and of course are easily distinguishable in section 

 from small Nematode cysts of the same size both by the 

 absence of the worm, the nature of the contents, and by the 

 structure of the capsule wall. As I have said before, all stages 

 of the growth of these masses are to be found, and since it 

 would be profitless to describe the gradual process of histo- 

 genesis which commence in masses of about the size shown in 

 PI. 5, fig. 45, I have only figured sections of three of the later 

 stages, the magnifications stated giving some idea of their 

 relative sizes. PI. 5, fig. 43 (xll2) illustrates an encapsuled 

 mass with tissue still quite undifferentiated, and PL 5, fig. 44 

 ( xll2) a larger similar mass, and PL 5, fig. 45 ( x35) shows 

 a later stage of the worm after it has become too long for the 

 capsule and is consequently becoming coiled. The commencing 

 histogenesis is not indicated in the figure. In still later stages 



^ These early stages must be distinguished from sections through iierve- 

 tibres iii the mesentery, which are very numerous and are often twisted 

 into lumps of about the same size as the masses, and in some cases are so 

 small as to resemble unicellular bodies. 



