129 
dency for more to approach the lower limit. In these measurements 
only fully mature individuals were considered. The living animals are 
so translucent that the smaller individuals can be distinguished by the 
unaided eye only with difficulty. The larger individuals have a very 
light milky appearance while in one or two instances a slight orange tint 
was seen. After fixation and preservation in alcohol the color is a uni- 
form translucent white. 
The hooks of this species (fig. 1) differ radically in shape from 
those of the other members of the genus. The portion of the hook 
protruding beyond the wall of the proboscis is very much smaller than 
the portion connected with the root. The shape of the root is also cha- 
racteristic of no other species that has been observed by the writer. 
freee? 
i, Q fees 
Sane 
‘= 
Figure 1. Neorkynchus gracilisentis n. sp. Proboscis (X 145), hooks (X 465), em- 
bryos ( 465). Camera lucida drawing. 
Instead of assuming the disc shape with the hook proper protruding 
from its anterior end this form has a much elongated and narrowed 
anterior portion which goes over gradually into the curved hook por- 
tion. Such is the condition found in the terminal and middle hooks, 
while the basal row contains slightly curved hooks with no roots (fig. 1). 
The cuticula is an extremely thin, non-cellular layer which covers 
the entire body. It has a fairly uniform thickness of about 0,001 mm. 
The subcuticula comprises the greatest part of the body-wall. In thick- 
ness this layer ranges from 0,017—0,030 mm. There is not the evident 
arrangement of this layer into a fibrous and a granular region as Kaiser 
(1893, pl. 2, fig. 10) has so clearly figured for Echinorhynchus angustatus. 
Within the subcuticula are found two types of canals. The dorsal and 
the ventral longitudinal canals extend from the base of the proboscis 
posteriad to the end of the body. These two canals are in direct com- 
munication with each other through a system of regularly arranged 
circular canals which are much smaller than the longitudinal trunks and 
differ from them in that they frequently branch and may occasionally 
anastomose. The body musculature is not very strongly developed. 
12* 
