32 Professors Clapar^de and Panceri on an Alcioptd, 



The larva3 of the most advanced stage which we have ob- 

 served are a centimetre long, with about thirty-six segments. 

 The upper antennse are elongated and somewhat porrected, 

 while the lower ones retain the form of tubercles. The eyes, 

 now more amply developed, have the form which they exhibit 

 in the adult Alciojye^ and, in conjunction with the lobes of the 

 head, have the faculty of executing movements which change 

 the direction of their axis. Except the hindmost pairs, which 

 still want them, the feet are furnished with setge, as has been 

 stated already, and as is shown in the figures. 



In all these larvae, besides the pigmentary spots of the dorsal 

 tubercles, there are also pigment-cells, more or less dark in 

 colom-, with fine ramifications, in the tegument of the head and 

 of the dorsal portion of the segments ; but these have not, 

 except in the first stage of the larvas, the regular arrangement 

 usual in the larvae of other Annelida. 



The larvae from 5 to 10 millims. long we have found in the 

 stomach of the Gydijjpe ; and we should have been inclined 

 to consider them to have been accidentally introduced, or as 

 the food of the Cydijpjpe^ if we had not obtained the others, 

 of smaller size, from the external tissues of the animal. This 

 seems to establish that they are parasites, inhabiting probably 

 the gastrovascular canals. Hence it seems to us a reasonable 

 supposition that the eggs, detached from the dorsal tubercles 

 of the mother, to which they appear constantly to adliere for a 

 certain period in the Alciope, as is proved to be the case with 

 other Annelida, are then swallowed by tlie Ci/dijjjje, and pass, 

 along with the serochyme, by means of the four principal 

 canals which branch off from the bottom of the stomach, into 

 the pleural canals, and from them into the smaller ones, 

 whence, as the growth of the larva goes on, they find their 

 way back into the larger canals and the stomach, out of which 

 they may easily escape or be expelled. Yet another hypothesis 

 may be considered — that the eggs are developed at large in 

 the water, and that the swimming larva penetrates into the 

 Cydijype — on which supposition the cilia may be regarded as 

 the instruments of locomotion. But, in either case equally, 

 whether the eggs are hatched in the body of the Cydippe or 

 out of this, as the cilia of the hexapod larvae are few and soon 

 disappear entirely, both these circumstances attest the parasitic 

 habits of the larvae. The prolonged existence of these organs 

 in swimming larvae, and their persistence in some parts of a 

 great number of adult Annelida, and even of some adult ani- 

 mals of the same family to which our larvte belong, corrobo- 

 rate the importance of this character, which is iutinuUely 

 related to the particular mode of life which we liave described. 



