31. 



siderably modified possibly to meet the sha^-o find needn cf 

 the cercaria or of the adult echincstotae. 



The study of the develo-v;i ->nt f the bladder in the 

 ceroaria of ^rUncMatoinun rQVolutum proved to be interesting 

 an. v > 3pra*i definite results. The first appearance of 

 the blndder - r -viy :;ari cf the <?xoretory syotem was seen 

 in a ^r:i o-.ll C.l.'H ri.i* long ruid C.1C4 mm. ^ride (fig* 37). 

 It irj .iur,t oomtaeuooci t,- ; ig from th t^pio-xl round 



germ ball* At this time two widely separat^d tubes extend- 

 ing nearly the entire length of tho body are present* At 

 the anterior end the? tubes appear tc ^nd in f?. ?ane ^ells which 

 oould not be clgrrly distinguished, due to the lank of 

 movement of th*ir oilia* )fi tube clearly rauet function 



independently of the other ^inn thv. Vo ex^r<?tory pores 

 are no^' J> ram. ^p^rt* xthen the ersbryo reaohes lengtlx 



of 0280 irn. the gunners ar* distinct; th*Miitf**r?tive y*tea 

 is fairly *!! developed; th^ triil has Commenced to differen- 

 tiate fro the body, and the excretory pores n^-* olo^-ir 

 to i- being cnly 0*018 oam*' apart (fig* 3B). #ien the 



embrvo ipt C.X6C mm. Tone th^ dig**tive Byr.tem is comul^t*. 

 At this time the inner surface rf the "/nllo of the excretory 

 tubes nearly touch eadv otJi-ir (fig. 39) a short distance 

 above the excretory pores. The tail is now quite decidedly 

 differentiated from the body. At about one-fourth the diatanc 

 from th-* base of the body to the end of the t<Ul the 

 excretory tubules bend alraoRt v^t right "ingles and empty 

 latrilly. .Figure 42 shows th<* right- >ialf of this r-risiitive 

 muscular bladder in various ah^pes, dr-iwn wi*t>iih a few 

 seconds of 'aoh e'U'ier* Those welli'n^s rr bulbs give evidence 



