382 GILMAN A. DREW 
The stains are not permanant, but when kept in the dark will 
last for some months. Formalin will harden gelatin, so mounts 
of formalin specimens become quite permanent, unless they are 
kept in a very damp place without being sealed. 
The spermatophore is very turgid and elastic. This is due 
to the outer covering, the outer tunic (fig. 2, OT), which is a 
tough and elastic membrane. It is transparent, rather thin, 
and of about even thickness except at the extreme anterior 
end, where it becomes thickened and sculptured for the attach- 
ment of membranes of the ejaculatory apparatus, and where 
it is modified to form the cap (C) covering the oral end. The 
cap ultimately loosens and allows the spermatophore to ejacu- 
late. The name cap which is applied to the portion that covers 
the oral end is somewhat confusing. The covering is formed 
by winding and cementing down around this end a thin leaf of 
outer tunic material which is continued as a long thin thread, 
the cap thread (CT), from the oral end of the spermatophore. 
This thread serves to loosen the winding of the cap when it is 
pulled, and ejaculation processes are immediatley started. 
The outer tunic gives the strength and elasticity to the sper- 
matophore. The very great turgidity is due to the strain to 
which this tunic is subjected. When this tunic is punctured 
or cut, the contents escape rapidly and the tunic shrinks be- 
cause of its elasticity. 
Inside the outer tunic is the middle tunic (figs. 1 and 2, MT). 
This is closely applied to the outer tunic, thickened over the 
whole aboral end and gradually thins out orally, after the sperm 
mass is passed. The aboral portion is rather thick and granular, 
but transparent. After the region of the cement body is reached. 
the granular character is lost, and it is very difficult to deter- 
mine whether a membrane is present or whether the space is 
filled with liquid. However, it can sometimes be easily traced. 
Under certain conditions of distension or ejaculation of the sper- 
matophore, a line appears that can be accounted for only as 
the inner border of such a membrane. This portion is quite 
transparent, differing greatly in appearance from the granular 
membrane in the aboral end, but under favorable conditions 
