CUMACEA. 303 



p. 219); the metamorphosis of the Alima series would thus appear 

 abbreviated by the suppression of the Erichthoidina stages. The 

 further course of development in the Alima form agrees with that 

 in the Erichthus forms. 



The connection of the various ontogenetic forms with definite genera and 

 species of Stomatopoda can hardly be accomplished on account of the difficulty 

 of obtaining continuous series of stages. It must, however, be considered 

 probable (Brooks, No. 84) that the Alima and Alimerichthus forms represent 

 the larvae of the genus Squilla. W. Faxon, at least, succeeded in producing 

 from an advanced Alima the young stage of Squilla empusa. Brooks believes 

 that he can recognise in Alimerichthus the larvae of species closely related to 

 Squilla microphthalmia. Still more difficult to decide is the question in what 

 way the Erichthus forms which merge one into the other are to be distributed 

 among the other Stomatopoda. Claus, however, has related certain Erichthus 

 forms with high, laterally compressed frontal spine and short carapace (Pseude- 

 richthus, Brooks) to the genus Pseudosquilla, while, on account of the slightly 

 arched dorsal shield, the long rostrum and the closely approximated, posterior 

 lateral spines, and, above all, the absence of teeth on the terminal joint of the 

 large prehensile maxillipede, he has related other forms (Gonerichthus, Brooks) 

 to Gonodaciylus. Another series of larval forms {Erichthus Duvauccllei and 

 multispinosus) characterised by a strongly arched dorsal shield, a flat abdomen, 

 widely separated posterior lateral spines, as well as ventrally incurved lateral 

 edges of the dorsal shield, may be referred, with Brooks, on account of the 

 presence of numerous teeth on the terminal joint of the second maxillipede, 

 to Lysiosquilla, and may therefore be called Lysioerichthus. Brooks was able 

 to observe, in the case of a larva nearly related to Lysioerichthus multispinosus, 

 the direct transition into Lysiosquilla excavatrix. With regard to the difficulty 

 of classifiying the other larval forms, it must be borne in mind that our 

 knowledge of the adult forms is by no means complete, as has been proved by 

 occasional discoveries (such as that of the remarkable Pterygosquilla found 

 by Hilgendorf). Fossil Stomatopoda have also recently become known. 



12. Cumacea. 



The Cumacea, which occupy an intermediate position between the 

 Schizopoda and the Arthrostraca (especially the Anisopoda), show 

 an abbreviated and fairly direct form of development. As in 

 the Mysidae (p. 257), metamorphosis is confined almost entirely 

 to stages passed through within the brood-cavity of the mother. 

 The embryos, by their dorsal curvature, as well as by the presence 

 of the dorsal organ, recall the Isopoda. The compound eye, which 

 in the adult is usually unpaired, arises by the fusion of paired 

 rudiments. The young that emerge from the brood-cavity are still 

 without the last pair of thoracic limbs, and, in this respect, resemble 

 the Isopoda. Only the sixth pair of pleopoda is well developed. 

 The five anterior pairs are wanting in the young (as is also the case 

 in the Anisopoda), and are, as a rule, only partly developed in the 

 adult males (Dohrn, No. 96). 



