6o COE 



Color. — The worms are very pale, whitish or pale yellowish in color, 

 with dark intestinal lobes. 



Size. — Very small, not usually more than 5 to lo mm. long and 

 0.5 to I mm. in diameter when sexually mature. 



Ocelli. — Wanting. 



Proboscis. — The proboscis sheath reaches nearly to the end of the 

 body. The proboscis is remarkable for its enormous size as com- 

 pared with the size of the body — when everted its diameter is practically 

 equal to that of the body itself, although it is then comparatively short. 

 Its armature consists of a central stylet with rather slender basis, and 

 of two pouches of accessory stylets. The basis of the central stylet 

 is slightly swollen and somewhat sharply truncated posteriorly. Each 

 pouch contains 2 or 3 long, slender and delicate accessory stylets. 



In cross section of the proboscis the inner and outer circular muscu- 

 lar layers appear as usual. The intervening layer of longitudinal mus- 

 cles, however, is divided into two secondary layers separated by a thick 

 sheet of nerves and connective tissue. The nerves appear to be more 

 or less confluent, and not separated into a definite number of longitudi- 

 nal cords as in most other species of Tetrastemma. This appearance 

 may be partially due, however, to the action of the formalin in which 

 the worms were preserved. 



Sense Organs. — The cerebral sense organs are very well developed, 

 and unusually voluminous as compared with the other organs of the 

 head. They lie in front of the brain, and extend posteriorly on the 

 ventral side of the brain lobes as far as the ventral commissure. Each 

 sense organ communicates with the exterior by a small canal passing 

 obliquely forward to open on the lateral margin of the head. 



The brain is of small diameter, but its extent antero-posteriorly is 

 comparatively great. 



Reproductive organs. — The individuals are hermaphroditic, and 

 probably to some extent protandric although there is considerable varia- 

 tion in this respect. One of the individuals sectioned was filled with 

 ripe spermaries only, but all the others possessed enormous ova, with 

 the spermaries disposed irregularly. The mature ova were fully two- 

 thirds the diameter of the body, and hence were arranged at irregular 

 intervals in a single row. Where the ova were mature the spermaries 

 were smaller and contained much fewer spermatozoa than in those in- 

 dividuals which were without large ova. Many of the spermaries had 

 ducts which pierced the muscular layers to reach the dorso-lateral sur- 

 faces of the body. In some cases where these ducts were fully formed, 

 and the spermatozoa therefore mature, the ova in the same individual 

 were but half grown. The sexual products were mature in July. 



