A STUDY IN MORPHOLOGY. 103 



Wiss. Zool., xxi., 1871), DoHEN describes the " Larve eines unbekannten Krebses" 

 from the Indian Ocean (p. 377), which is shown in his plates 29 and 30, tigs. 62 

 to 67. In his ' Crustacean- System ' (taf. iv., figs. 2 to 7) CLAUS gives much more 

 satisfactory figures of what appears to be the same larva, and speaks of it as a 

 " Phyllopodenahnlichen Protozoea unbekannter Herkunft." Its close resemblance to 

 the Protozoea of Lucifer renders it extremely probable that it is the Protozoea of a 

 Sergestid, and as the Protozoea of Lucifer and that of Seiyestes-a,re known, this must 

 be the larva of Acetes, or of some closely-related unknown form. 



The carapace is nearly smooth, rounded, and there is no trace of a rostrum, and it 

 makes more than three-quarters of the total length of the body. 



The compound eyes are present and well developed, but they are sessile, and there 

 is no indication of the stalk. The first antenna is seven-jointed, and the two tei'minal 

 joints are thin and long. 



The second antenna is nearly twice as long as the first, and very thick. Its short 

 stout basal portion consists of two joints, and carries a short two-jointed exopodite, with 

 three long terminal non-plumose swimming hairs, and a very large twelve-jointed 

 endopodite with a long swimming hair at each joint. 



CLAUS'S figures show that the appendages at the back of the antenna? are very much 

 like those of Lucifer, and the same ones are present ; that is, the mandibles, first and 

 second maxillse, and first and second maxillipeds. 



The hind body is segmented, and ends in a broad, fiat, deeply-cleft telson, with six 

 pairs of irregularly plumose hairs, the third pair very much longer and thicker than 

 the others. 



A comparison of CLAUS'S figure with tig. 27 of this paper will show that most of the 

 ditferences between this unknown larva and the first Protozoea of Lucifer are of the 

 same kind as the ditferences between the Acetes Zoea (fig. 79) and the corresponding 

 stage of Lucifer (fig. 44). 



At a time when the eyes of Lucifer are rudimentary and sessile they are perfect and 

 stalked in Acetes, and at a time when they are entirely absent in Lucifer DOHEN'S 

 larva has them sessile and rudimentary but distinct. 



The Zoea of Acetes, like this larva, has its telson deeply forked ; its hairs are 

 plumose, and the third is much longer than the others. These resemblances, and the 

 great length of the carapace, render it very probable that this unknown larva is the 

 Protozoea of Acetes. 



I will now continue my description of the appendages of the Zoea. 



The first antenna (fig. 77, A) is uniramous, and it consists of a long, cylindrical, 

 two-jointed shaft, and a single short flagellum, which shows obscure traces of a division 

 into three joints. The basal joint of the shaft is a little more than half as long as the 

 second joint, and it carries a single short sharp hair on the inner side of its distal end. 

 The second joint has two much longer hairs on its distal end, and one about half way 

 between its ends. The flagellum makes about one-fifth of the total length of the 



