168 W. Lilljeborg on the Genera Peltogaster and Liriope. 



larvae in the lateral apophyses of the anterior part of the body ; 

 and as the mouth is situated in this organ, it appears that it also 

 has been formed by the transformation of the tubular mouth of 

 the larva. It presents different forms in the different species, 

 and may furnish distinctive characters. Where it is fixed, the 

 epidermis is always firmer and thicker, and it sometimes even 

 extends over the epidermis like a shield (fig. 8 b). Sometimes 

 there is only a ring of firmer tissue on the epidermis round its 

 base. When the Peltogastri which have the organ of adhesion 

 rounded, and not ramose, are separated from the skin of the 

 Pagurus, the latter exhibits a round hole at the point where 

 the organ of adhesion was fixed; through this aperture they no 

 doubt suck their nourishment. 



The newly-hatched larva (fig. 16) is less elongated than the 

 larvae of other Cirripedes, The posterior part of the body is not 

 pointed, but rounded and obtuse, as in the larvae of the Lernaeidae 

 and Copepoda. But the larva of Peltogaster differs from the 

 latter by an apophysis projecting from each side of the front of 

 the body, and issuing from the lower surface. In the very 

 young larvae this is attached to the body in such a manner that 

 it is difficult to see it ; but as the second pair of antennae are 

 formed in these apophyses, and it is with these that the Cirri- 

 pede afterwards adheres, it is evident that the apophyses are of 

 the greatest importance, and their presence may be regarded 

 as characterizing the animal. The larvae of Cirripedes are 

 distinguished from those of the Lernaeidae and Copepoda by the 

 early presence of the first pair of antennae not in the form of 

 legs. The author has been unable to discover these antennae in 

 newly-hatched larvae or in those still contained in the eggs*. 



No specimen of this genus has hitherto been discovered ex- 

 cept upon species of the genus Pagurus. They are usually fixed 

 upon the left side of the abdomen, in such a way that the aper- 

 ture leading into the cavity of the body is turned towards the 

 anterior part of the Pagurus, and consequently towards the 

 aperture of the shell in which the Pagurus resides. This is pro- 

 bably to enable the young to escape as rapidly as possible. The 



* According to Claus (Archiv fur Naturg. 1858, p. 1, and " Ueber den 

 Bau und die Entwickelung parasitischer Crustaceen," Cassel, 1858, p. 5), 

 the parts of the mouth in the Copepoda are formed from the third pair of 

 feet of the larvae, and the antennae from the first and second pairs. As, 

 according to Darwin, the feet in the larvae of the Cirripedes have no sig- 

 nificance as future antennae, the appendages of the mouth of the Cirri- 

 pedes, by analogy with the order of development of parts in the Copepoda, 

 should be formed from the first pair of feet of their larvae. But Darwin 

 thinks that this pair of feet corresponds with the second pair of feet or 

 cirri in the developed animals. There is here, at any rate, a great difference 

 in the development of the Cirripedia and Entomostraca. 



