220 CRUSTACEA. 



shell-valves is cast first, the thorax and the inner mantle-cavity losing their 

 cuticle later. 



In most of the Tlioracica, metamorphosis seems to run the course above 

 described. Only in individual cases is it more abbreviated. Thus, according to 

 KoREN and Danielssex (No. 48), the larvae of Anclasma squalicola jmss 

 througli the greater part of their metamorphosis within the mantle-cavity. 

 KossMANN, however, describes the Nauplii of these forms whose larvae, according 

 to the above authors, when hatched, are provided with six pairs of limbs. 

 Pagenstecher has rightly connected this feature with the attachment of 

 Anelasma to sliarks. Still more ablireviated is the metamorphosis of Scalpellum 

 Stroma, the Cypris stage of wliich, surrounded by the Nauplius cuticle, was 

 found by Hoek (No. 45) even within the egg-envelope. 



B. Abdominalia. 



The metamorphosis of Alcippe, a form which bores into the 

 columella of the shells of Fusus and Buccijium (especially when 

 these are inhabited by Pagurids) seems to agree in essentials with 

 that of the Thoracica. The Nauplii were first described by Hancock. 

 The Cypris stage described by Darwin (No. 40) is distinguished by 

 the possession of six pairs of thoracic limbs, a fact worth mentioning 

 in contrast to the reduced number and shape of these limbs in the 

 adult ; only four pairs of these are retained, the first as a palp, 

 the second biramose, and the third uniramose. 



In Kocldorine, which bores into the shell of Haliotis, Noll 

 (No. 56) found two kinds of larval forms, a small form i^rovided 

 with adhering antennae, but without a mantle, and a larger form 

 having a bivalve shell and resembling the Cypris stage. It is 

 probable that the metamorphosis here is closely related to that of 

 the nearly allied genus Cryptophialus. 



The metamorphosis of Cryptophialus, first described by Darwin 

 (No. 40), is greatly abbreviated. The egg here passes almost direct 

 into the Cypris-\\kQ larval form. There first arises from the oval 

 egg a larva in which two processes can be recognised as the rudiments 

 of the adhering antennae. A third jjrocess indicates the posterior 

 end of the body. At a later stage, the adhering antennae are ap- 

 proximated, while the body assumes generally a more pointed egg-like 

 shape. From this stage the Cypris form emerges, in which can be 

 distinguished the mantle-fold, the paired eyes, and the well-developed 

 adhering antennae. The rudiments of the thoracic limbs are here 

 wanting, but three pairs of setae are found on the abdomen. These 

 larvae creep about by means of the adhering antennae in the mantle- 

 cavity of the mother, and finally change into the adult form. For 

 the development of the stalk in these forms, see p. 218. 



