76 HISTOKY OF CRUSTACEA. Chap. YIIT. 



pliium dentatum, n. sp.. and the last abdominal segments 

 and tlie tail in BracJiysceliis,^^ or where one or more 

 segments are deficient, as in Dulichia and the Caprellse, 

 we find the same fusion and the same deficiencies in 

 young animals taken out of the brood-pouch of their 

 mother. Even peculiarities in the structure of the 

 limbs, so far as they are common to both sexes, are 

 usually well-marked in the newly hatched young, so 

 that the latter generally differ from their parents only 

 by their stouter form, the smaller number of the an- 

 tennal joints and olfactory filaments, and also of the 

 set86 and teeth with which the body or feet are armed, 

 and j)erhaps by the comparatively larger size of the 

 secondary flagellum. An exception to this rule is pre- 

 sented by the Hyperinse which usually live upon Aca- 

 lephse. In these the young and adults often have a 

 remarkably different appearance; but even in these 

 there is no new formation of body-segments and limbs, 

 but only a gradual transformation of these parts.^^ 



^2 According to Spence Bate, in Bracliyscelus crusculum the fifth 

 abdominal segment is not amalgamated with the sixth (the tail) but 

 with the fourth, which I should be inclined to doubt, considering the 

 close agreement which this species otherwise shows with the two 

 species that I have investigated. 



^3 In the young of Hyper i a galba Spence Bate did not find any of the 

 abdominal feet, or the last two pairs of thoracic feet, but this very 

 remarkable statement required confirmation the more because he 

 examined these minute animals only in the dried state. Subsequently 

 I had the wished-for opportunity of tracing the development of a 

 Ilyperia which is not uncommon upon Ctenophora, especially Beroe 

 gilva, Eschsch. The youngest larvse from the brood-pouch of the 

 mother already possess the whole of the thoracic feet ; on the other 

 hand, like Spence Bate, I cannot find those of the abdomen. At first 

 simple enough, all these feet soon become converted, like the anterior 



