264 C. H. MARTIN. 
(c) Sagittocysts are confined to the Accela, and consist of 
a membrane surrounding a cavity in which a solid needle- 
shaped body lies. . 
They seem to occur only in the genital regions at the period 
at which the male sexual products are mature, and are 
regarded as “ Reizmittelm bei der Begattung.” 
(d) Nematocysts. 
Von Graff summarises his views as to the connection ~ 
between these various structures in the following passage : 
“Von den als Ausganspunkt erscheinendem Pseudo- 
rhabditen, welche sich weder gegen das ungeformte Secret 
der Hautdriisen einer noch gegen die strukturlosen Rhab- 
diten andererseits scharf abgrenzen lassen, fiihrt auf diese 
Weise, durch solche Rhabdoiden bei welchen sich ein 
hyalinen Mantel von der Kornigen Zentralmasse scheidet 
(Rhammiten) die schrittweise Differenzierung zu Sagitto- 
cysten und den verschiedenen formen von Nematocysten— 
Hine Anschauung die ich schon 1874 ausgesprochen habe.” 
The following list contains, I believe, the names of all the 
Turbellaria which have been described as possessing nemato- 
cysts. These which I have been able to examine are marked 
with an asterisk : 
RHABDOCELA. 
Section 1.—HYSTHEROPHORA. 
Fam. CATENULID2. 
Microstoma lineare.* 
Hf giganteum.* 
Es rubromaculatum.* 
x papillosum.* 
Stenostoma sieboldii.* 
Section 2.—LECITHOPHORA. 
Sub-section : KaLyproRHYNCHIA. 
Fam. PoLycystiDIp@. 
Polycystis naegelii.* 
i mamertinus.* 
