166 Mr. C. Spence Bate on the Affinity of Praniza with Anceus. 



whicli it is stated that Praniza aud Anceus are but two ages of 

 one and the same animal ; that, after having lived during a cer- 

 tain time under the form of Praniza, it assumes that of Anceus, 

 and in this latter stage gives birth to young Praniza. The 

 reverse of this appears to have been the idea of Mr. A. White, 

 when he prophesied, in his recent ' Manual of the British Crus- 

 tacea,' " that there is some likelihood that Anceus may prove to 

 be one of the stages of Praniza." 



M. Hesse's statements rest upon no hypothesis. They are the 

 result of facts that he himself has witnessed, drawings of which 

 accompany his memoir. The whole are now being submitted 

 to a commission composed of MM. Dumeril, Milne-Edwards, 

 and Coste*. 



In studying the smaller forms of Crustacea, I have obtamed 

 many specimens of each of the animals in question ; and though 

 I have hitherto confined myself to the study of the Amphipoda, 

 I am induced not to allow the data I possess upon the question 

 to remain any longer concealed. 



Before entering upon a discussion of the subject, it will be 

 desirable to have a clear idea and just appreciation of the forms 

 of the separate parts as well as of the general structure of both 

 animals. I shall therefore commence by an examination of the 

 adult Praniza. 



The cephalon is quadrate. The eyes, sessile and prominent, 

 are situated upon each side of the head. The antenna are four, 

 nearly equal. Posterior to the cephalon are two distinct segments, 

 each supporting a pair of legs directed anteriorly. Then follow 

 three membranous segments fused into one large oval division. 

 This, together with the two preceding segments, and one, too 

 insignificant to be observed by unassisted vision, form iheji^^reion. 

 It consists of six segments only. So also the pleon, which is 

 much narrower than the pereion, and laterally carries two pairs 

 of foliaceous appendages upon each of the six segments. 



The general outline of the head appears to converge to a 

 point anteriorly. This has universally been the accepted form 

 of the animal,— a form that is due, not to the shape of the 

 cep)halon, which is, as I before observed, square, but to the shape 

 and position of the labium and organs of the mouth. 



The labium (PL VI. fig. 7 d") in Praniza is an important organ. 

 It is large, and projects horizontally forwards. The anterior 

 margin is concave, aud considerably narrower than the posterior. 

 Prom the centi-e of the anterior edge, after having traversed the 

 inferior surface of the organ, projects a small siphon. 



* Since tliis paper has been in the press, the report confirming M. Hesse's 

 views has been presented to the Academy by M. Mdne-Edwards. bee 

 Annals, 3rd scries, No. 8. p. 164, 



