30 Professors Clapar^de and Panceri on an Alciopidj 



and which commonly, and sometimes in multitudes, inhabit 

 the external surface of nearly all the Acalephse of the ocean 

 and the Mediterranean ; but the coexistence of others of a 

 larger size, and the presence of minute Annelida in the sto- 

 mach, have led us, with the help of direct observations, to the 

 conviction that all these parasites are larvae of Annelida, which 

 the development and pigment of the eyes early indicated to 

 belong to the family of the Alciopids. 



The smallest of these larvaB, which we will call the first 

 stage, and which scarcely attain the length of 1 millim., have 

 the head not yet distinct from the rest of the body, and with- 

 out any vestige of appendages. The eyes are not protuberant, 

 but represented by a small crystalline lens, nearly spherical, 

 posterior to which and in the interior is seen a layer of pig- 

 ment. The body, elongated and with scattered pigmentary 

 spots, has no indication of the division into segments, except 

 in the presence of three pairs of conical feet, having each two 

 short projecting setse : vibratory cilia were observed in two 

 tracts — from the mouth to the middle of the abdominal surface, 

 and again in the extreme posterior region. The opening of 

 the mouth has the form of a simple fissure, to which succeeds 

 a muscular tube, then a spacious gastric sac, open behind. 



In the larvae which we call the second stage, the head 

 acquires a greater development ; the eyes become prominent, 

 and, in addition to the crystalline and the layer of pigment, 

 show a ring which defines their outline. The oral segment has 

 now become apparent, furnished with two rudimentary appen- 

 dages ; and the tube now becomes gradually exsertile from 

 the mouth. The body is more elongated, has lost the cilia, 

 and, besides the three rings furnished with setigerous feet, 

 shows the outlines of the consecutive segments. 



The larvaj in the third stage attain the length of 2-3 millims.; 

 and the largest of them have four tubercles, which are the 

 first vestiges of the antennae. The eye is further increased in 

 volume, and the choroid is gradually acquiring pigment in its 

 posterior segment. The other feet, additional to the three 

 primitive pairs, become furnished with setae, and are gradually 

 developed, so that sixteen segments or more may now be 

 counted, the anterior ones possessing prominences and pig- 

 mentary spots, representing respectively the cirrus and the 

 tubercles of the dorsal region in its more advanced stage. 



Anatomie u. Entwicklung wirbelloser Thiere an der Kiiste von Nor- 

 mandie, 1863, p. 12, and the investigations on the same subject by Prof. 

 A. Costa (Rendiconto d. R. Accad. d. Sc. Fisiche e Matematiche di Napoli. 

 fasc. 4, Aprile 1864). 



