HOUGHTON, ON THE GLOSSIPHONIDiE. 35 



converging towards the anterior extremity ; in some indivi- 

 duals, and frequently in the species G. hyalina and G. com- 

 planata, the anterior pair are wanting, and the order of 

 arrangement is confused. The posterior acetabulum is large 

 and round ; the genital openings, of which the male is the 

 upper, occur somewhere between the twenty-fifth and twenty- 

 eighth ring of the body ; the digestive system consists of a 

 stomach, having from five to seven pairs of gastric cseca ; the 

 intestine has uniformly four cseca. All the British members 

 of this family are strictly oviparous ; one is surprised to read 

 in Diesing's ' Systema Helminthum' (vol. i, 446), '^'ut plurimum 

 vivipara." They are incapable of swimming, and move from 

 place to place like the caterpillars called geometric ; this is 

 particularly the case in the species G. tessulata and G. mar- 

 ginata, which are very active in their movements. Most of 

 the species roll their bodies up like Onisci if taken out of the 

 "water and handled. They inhabit brooks and ponds ; and 

 though all the species above enumerated are, as stated by 

 Diesing, " aquarum dulcium incol(B," they are frequently found 

 in water which is anything but sweet. None of the British 

 species can be truly said to be parasitic, though any of them 

 may be occasionally found upon the bodies of aquatic animals, 

 on the juices of which they feed. I purpose now to make a 

 few observations on — 



1st. The structure of the Glossiphons. 



2dly. Their mode of increase, and the development of 

 the embryos. 



1st. The normal form of the body, when at rest is pear- 

 shaped, the posterior extremity being rounded and obtuse, 

 the body narrowing somewhat suddenly towards the anterior 

 extremity, but different species vary slightly inter se ; the 

 mouth, which is always subterminal and bilabiate, and with- 

 out teeth, leads to the proboscis by a delicate, transparent, 

 membranous oesophagus, with which it is continuous, and by 

 which it is included ; this membrane is drawn back over the 

 proboscis, when it is extended, in a manner similar to the 

 unfolding of a glove from the finger ; the form of this exsert- 

 ile tube is cylindrical, minutely lipped or segmented at the 

 apex, and commonly bulbous at the base; it is of a sub- 

 cartilaginous consistency, and supplied with powerful mus- 

 cles, by means of which it is worked ; under the microscope, 

 the reticulated, muscular structure is observable, more espe- 

 cially on the bulbous portion of the proboscis. It is by 

 means of this tube that the animal pumps out the juices of 

 its victims, its labiated apex seeming to act the part of a 

 mouth. There are some slight modifications of form in the 



