ii6 



CRUSTACEA SVNCARIDA 



characters are the entire absence of a carapace, and the freedom 

 of the eight thoracic segments, with eight free thoracic ganglia in 

 the nerve-cord ; the peculiar double series of plate-like gills ; the 

 structure of the alimentary canal; and the fact that the eggs, instead 

 of being carried in a brood-pouch, or affixed to the abdominal 

 limbs, are deposited under stones and among water-plants. 



Fig. 77. — Anaspides tasmaniae in natural position for walking, x 1. The last two 

 [lereiopods point backwards and are overlapped by the first two pleopods. 



The Peracaridan features, uniting it especially with the 

 Mysidacea, are the structure of the elongated heart, the filiform 

 spermatozoa, and the fact that no complicated metamorphosis is 

 passed through, the young hatching out in a condition similar 

 to, though possibly not identical with, the adult form. 



The Eucaridan, especially Decapodan, features are the 

 presence of an auditory sac on the basal joint of the antennules, 



1 This cliaracteristic is found in the Crustacea elsewhere only in the Argulidae 

 and certain Euphausiidae. 



