HOUGHTON, ON THE GLOSSIPHONID^. 39 



that this act does take place in the case of G. tessulaia, but 

 further observations on this point are needed before we can 

 decide whether all these animals are self or mutually im- 

 pregnating, or how far the presence of two individuals is 

 necessary for the purpose of generation. 



If specimens of these worms be procured early in March, 

 and kept in vessels of water, ample facility will be aiforded 

 of noticing the manner of depositing the ova, the period of 

 incubation, and the gradual development of the young from 

 the vitellus to the perfect individual ; and the extreme trans- 

 parency of very young indi^dduals renders a study of their 

 structure easy and delightful. 



G. hyalina and G. bioculata do not sit upon their ova, but 

 carry them about with them on the abdominal surface. The 

 ova and young of G. bioculata are very effectually protected 

 by, means of the folding inwards of the sides of the parent, 

 which are thus made almost to meet and to form a sort 

 of pouch ; this fact will, I believe, explain the error of some 

 who have asserted that the Glossiphons are, in some cases, 

 viviparous. 



The young are hatched, i. e. the partially developed embryo 

 leaves its pellucid, gelatinous envelope in about ten days 

 after the ovum is deposited ; the number of vitelli in each 

 envelope is variable, not only in the different species, but in 

 individuals of the same species and in the individual itself. 

 In G. complanata and G. marginata three to fifteen vitelli 

 may be contained by the delicate covering. G. tessulata is 

 the most prolific of all the species ; I have counted a hundred 

 and twenty young ones attached to the parent. The young, 

 for some little time after they are perfectly formed, continue 

 tied to their '' mother^s apron-strings,'' which they generally 

 leave when they are about six weeks old. 



The Glossiphons, like all other animals, and especially 

 such as are aquatic, have their external and internal parasites ; 

 upon the curious, horn-like plate of membrane in the neck of 

 G. bioculata it is a very common thing to find a species of 

 Epistylis firmly attached to it. I have never observed this 

 parasite either on any other Glossiphon or on any other 

 part of G. bioculata but on the cervical plate. If it has 

 never been described, I propose to call it Epistylis Glossi- 

 phoni(E. ^ 



I am quite unable to form the most remote conjecture as 

 to the use of the plate referred to above. It is situated and 

 opens out at the upper part of the neck. This membranous, 

 cup-shaped body is characteristic of G. bioculata. 



