ON APPENDICULARIA FLABELLUM 451 



from the animal, and then becoming diffused in the surrounding 

 water. This circumstance, indeed, appears to have furnished his 

 principal reason for believing these bodies to be what the name 

 indicates. 



" The spermatozoa have elongated and pointed heads about 

 I -sooth of an inch in length, and excessively long and delicate filiform 

 tails. 



" Mertens describes as an ovary, two granulous masses, which 

 he says lie close to the vesiculje seminales, and have two ducts, which 

 unite and open into this ' ovisac' 



"This appears to me to be nothing more than the granulous 

 greenish mass of cells and undeveloped spermatozoa, which exists in 

 the testis at the same time as the orange-red mass of fully-developed 

 spermatozoa. 



" I saw nothing of any ducts, nor do I know what the ' ovisac ' can 

 be, unless it be a ftirther development of an organ which I found 

 in two specimens (fig. 3 g), consisting of two oval finely-granulous 

 masses, about i -300th of an inch in diameter, attached, one on each 

 side of the middle line, to the dorsal parietes of the respiratory cavity, 

 and projecting freely into it. 



" Still less am I able to give any explanation of the extraordinary 

 envelope or ' House ' to which, according to MERTENS,^ each Appen- 

 dicularia is attached in its normal condition. I have seen many 

 hundred specimens of this animal, and have never observed any trace 

 of this structure ; and I have had them in vessels for some hours, but 

 this organ has never been developed, although Mertens assures us 

 that it is frequently re-formed, after being lost, in half an hour. 



" At the same time it is quite impossible to imagine, that an 

 account so elaborate and detailed, can be otherwise than fundament- 

 ally true, and therefore, as Mertens' paper is not very accessible, I 

 will add his account of the matter, trusting that further researches 

 may clear up the point. 



" The formation of the envelope or ' Haus ' commences by the 

 development of a lamina from the ' semicylindrical organ ' (ganglion ?). 

 This, as it grows, protrudes through the opening at the apex of the 

 animal (respiratory aperture). Its corners then become bent back- 

 wards and inwards, and thus a sort of horn is formed on each side, 

 the small end of which is turned towards the apex of the animal, 

 while its mouth looks backwards, downwards, and outwards. 



^ I have given this passage at length in order that others may be led to seek its explana- 

 tion. Leuckart and Gegenbaur have been as unsuccessful as myself in finding any such 

 structure ; but that it should be purely imaginary seems past belief. 



G G 2 



