182 HUXLEY, ON APPENDICULAR! A FLABELLUM. 



" Between the two lobes, posteriorly, the iutestine (A) commences, and 

 passing upwards (or forwards) terminates on the dorsal surface just in 

 front of the insertion of the caudal appendage (/). 



" The heart lies behind, between the lobes of the stomach. I saw no 

 corpuscles, and the incessant jerking motion of the attached end of the 

 caudal appendage rendered it very difficult to make quite sure even of the 

 heart's existence." . 



" The caudal appendage (A) is attached or rather inserted into the body 

 on the dorsal surface just behind the anus. It consists of a long, appa- 

 rL-ntly structureless, ti-ansparent, central axis (m), rounded at the attached, 

 and pointed at the free end. This axis is enveloped in a layer (o) of lon- 

 gitudinal, striped, muscular fibres ; which form the chief substance, in 

 addition to a layer of ijolygonal epithelium cells, of the broad alary expan- 

 sion on each side of the axis." 



" The only unequivocal generative organ I found in Ajipendicularia 

 was a testis (j)), consisting of a mass of cells developed behind and below 

 the stomach, enlarging so much in full-grown specimens as to press this 

 completely out of place, 



" In young specimens the testis is greenish, and contains nothing but 

 small pale circular cells ; but in adults it assumes a deep orange red- 

 colour, caused by presence of multitudes of spermatozoa, whose develop- 

 ment from the circular cells may be readily traced. 



" This orange-red mass, or rather masses, for there are two in juxta- 

 position, is described by Mertens as the ' Samen-behalter ' or vesiculaj 

 seminales. He describes them as making their exit, bodily, from the 

 animal, and then becoming diffused in the surrounding water. This cir- 

 cumstance, indeed, appears to have furnished his principal reason for 

 believing these bodies to be what the name indicates. 



" Tlie spermatozoa have elongated and pointed heads about l-500th of 

 an inch in length, and excessively long and delicate filiform tails. 



" Mektens describes as an ovary, two granulous masses, which he says 

 lie close to the vesicular 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 further development of an organ which I found in two 

 specimens (fig. 3 q), consisting of two oval finely-granulous masses, 

 about l-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 en- 

 velope or ' House ' to which, according to Mertens,* each Appendicularia 

 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 fundamentally true, 

 and therefore, as Mertens' paper is not very accessible, I will add his 



* I have given this passage at length in oi-der that others may be led to seek its 

 explanation. Leuckart and Gegenbaur have been as unsuccessful as myself in finding 

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



