870 The Crustacean Nebalia and its Fossil Allies, [November, 



traca, but when we consider the composite nature of the internal 

 organs as described by him, we wonder that he failed to appre- 

 ciate the independent, synthetic nature of the Phyllocaridan type 

 which, when we take into account the external as well as internal 

 organization, forbids our regarding Nebalia as a true Malacostra- 

 can, though the type of a group standing outside of, but nearer 

 to the Malacostraca than are the Phyllopods. 



The development of Nebalia. — Our knowledge of the develop- 

 ment of Nebalia is due to the distinguished Russian embryolo- 

 gist, who in 1868 published an elaborate account of the develop- 

 mental history of Nebalia gcoffroyi. Unfortunately the pamphlet 

 is in Russian, and only brief abstracts of it have appeared in Ger- 

 man. But as ample and well-drawn figures illustrate the work, 

 we can state the salient points in the ontogeny of this interesting 

 Crustacean. The yolk does not undergo total division, but by 

 the subdivision of a large polar cell the yolk becomes surrounded 

 by a layer of blastodermic cells. Soon after the rudiments of the 

 two pairs of antennae and of the mandibles bud out, the abdo- 

 men also being differentiated from the rest of the body (PI. xv, 

 Fig. 1). This is regarded as representing the free nauplius con- 

 dition of other Crustacea. At a succeeding stage (Fig. 2) the 

 two pairs of maxillae and two pairs of thoracic feet bud out ; and 

 in a stage immediately succeeding (Fig. 3) the palpus of the 

 mandibles elongates, the maxillae are two-branched, and seven 

 (or eight) pairs of thoracic feet are indicated. In a succeeding 

 stage (Fig. 4) Nebalian characters assert themselves ; such are the 

 carapace and large rostrum, the biramous anterior pair of anten- 

 nae, the unbranched 2d pair, the long mandibular palpus, the 

 absence of any rudiments of maxillipedes, and the eight pairs of 

 thoracic feet (baenopoda) and three pairs of abdominal feet (uro- 

 poda), all of which are now well developed. At this stage it may 

 be seen that, as in spiders, the 1st pair of thoracic feet may rep- 

 resent the 2d maxillae of insects transferred from the head to the 

 thorax; so in Nebalia, the three first of the eight pairs of tho- 

 racic feet may correspond to the three pairs of maxillipedes of 

 Decapods, which in early life, before the thorax is differentiated 

 from the head, may have remained afterwards as a part of the 

 thorax. An intermediate step is the retention in the Mysidae of 

 the last pair of maxillipedes or the 1st pair of thoracic feet, so 

 that these Crustacea have six pairs of feet. Moreover, Nebalia 



