THE EUPHAUSIACEA 249 



In other cases the ova are agglutinated together in a paired or 

 unpaired mass, which is carried attached to the sternal surface of 

 the thorax, close to the bases of the posterior thoracic legs. These 

 egg -packets are formed by some cementing material apparently 

 extruded along with the eggs, and bear no sort of morphological 

 resemblance to the brood-sac of the Mysidacea Avhich is formed by 

 the oostegites. 



DEVELOPMENT. 



With the possible exception of the genus Stylocheiron, where the 

 relatively large size of the eggs suggests an abbreviated meta- 

 morphosis, the Euphausiacea leave the egg in the form of a typical 

 nauplius, and reach the adult stage by a series of changes closely 

 parallel to those occurring in the metamorphosis of the Penaeidea 

 among the Decapoda. Glaus was the first to show that the forms 

 described by Dana as distinct genera under the names Calyptopis, 

 Furcilia, and Cyrtopia are successive stages in the development of 

 Euphausiacea, and Sars has been able to fill in, with considerable 

 detail for several species, the outline thus furnished. 



The newly hatched nauplius, as described by Metschnikoft" and 

 by Sars, has an oval unsegmented body, without shell-fold, and with 

 the three pairs of nauplius appendages in their typical form, the 

 first uniramous, the second and third biramous ; the median eye is 

 not developed till the next stage. The mouth is not at first open, 

 and there is no masticatory process on the base of the antenna 

 such as exists in Copepoda and Cirripedia. 



In the next stage the larva assumes the form of a metanauplius 

 (Fig. 144, A), showing rudiments of three additional pairs of ap- 

 pendages, maxillulae, maxillae, and first thoracic limbs ; the shell- 

 fold is defined posteriorly and partly envelops the hinder end of 

 the body. In later metanauplius-stages the third pair of appendages 

 (mandibles) lose their natatory character and become reduced to 

 the basal masticatory part, with only a very small rudiment to 

 represent the palp ; the shell-fold now projects in front as well as 

 behind and overhangs the head in a hood-like form. 



The metanauplius is succeeded by a series of Calyptopis- 

 etages (Fig. 144, B, C) characterised by the elongation of the trunk- 

 region and the differentiation of its somites in regular order from 

 before backwards. The thoracic somites are very short and crowded 

 together. The appendages already present become more fully 

 developed, and, later, the rudiments of the last pair of abdominal 

 appendages appear. The paired eyes develop but are covered at 

 this stage by the frontal hood of the carapace. 



In the next succeeding Furcilia-stages the paired eyes become 

 free and movable. The pleopods develop from before backwards 

 and, later, the anterior thoracic limbs. The Cyrtopia -stage is 



