CRUSTACEA DECAPODA. 203 



embryo in the ovum is compared with that of the River Crayfish (according to 

 Rathke's former work.) "Whilst in the River Crayfish the antennae, labrum, 

 and mandibles appear simultaneously with the abdominal tubercle, in the 

 present instance the appearance of the latter precedes that of the mandibles, 

 labrum, and antennae. In the River Crayfish the jaws appear before the 

 legs ; in this case the order is reversed. Whilst in the River Crayfish the 

 pairs of jaws and ambulatory legs, are already formed in the embryo 

 such as they afterwards appear, in the present case only three pairs of 

 jaws, and three pairs of bifid feet present themselves, which latter after- 

 wards become manducatory feet, and the future ambulatory feet are at this 

 time entirely wanting. The order of appearance of the eyes, heart, intestine, 

 liver, and of the carapace is nearly alike in both. When the young quits the 

 ovum, its eyes resemble those of the full-grown animal ; they are, however, as 

 yet sessile and extremely large. The antennae are short, and with few joints. 

 The rostrum on the carapace is as yet but little developed. The abdomen is 

 long in proportion, six-jointed, the caudal segment bilobed or spatulate. Legs 

 occur only on the thorax, and constitute three pairs of bifid feet. At the mouth 

 is a fleshy labrum, a pair of mandibles similar to those of the full-grown animal, 

 and two pairs of many-lobed maxilla?. As yet there is no trace of branchiae ; 

 they are not formed till later, and proportionately slowly, and the more 

 posterior they are, the later are they developed. The alimentary canal is 

 simple, the stomach a mere dilatation, without a trace of the cartilaginous 

 apparatus, which is present in that of the full-grown animal. The liver, 

 which in the adult state is formed of two lobes, each constituted of numer- 

 ous cfecal biliary vessels, presents at this time the appearance of a granular 

 mass, surrounding the commencement of the alimentary canal. 



The young of Porcellana lonyicornis has been observed by 

 Dujardin. (Rev. Zool. p. 187.) 



It exhibits a zoa-forin, resembling the young of Pagunts. It has two 

 pairs of antennae, in the mouth three pairs of jaws, viz., one pair of perfect 

 mandibles, and two pairs of maxillae, both the latter with palpi ; more- 

 over, at the posterior part of the cephalo-thorax, two pairs of bifid feet, 

 which, like the antenna. 1 , are beset with extremely fine feathering setae, 

 resembling those with which the rowing and branchial feet of the Eutomos- 

 traca are furnished, and which the author consequently regards as the 

 respiratory organs of the young Crab. Lastly, the posterior part of the 

 cephalo-thorax has, besides these, two lateral, elongated processes, directed 

 backwards, and corresponding to the dorsal spiculum of the other Zoas. 



Erdl ' Entwickelung des Hummereies, von den ersten 

 Veranderuugen im Dotter an bis zur lleife des Embryo/ 



