420 Dr. H. J. Hansen on the Morphology of the 



segments of the endopodite of the jaw ; in proportion to the 

 segments these lateral processes often become extraordinarily 

 large, greatly elongated, separated therefrom by an articula- 

 tion, and even sometimes transversely divided, inconsequence 

 of which it is only with ditSculty that they can be understood 

 when but a superficial examination is made. It is there- 

 fore necessary to trace the segments in the endopodite of the 

 maxillae in thoroughly cleansed preparations, and at the same 

 time to find out from which segment the chitinous lamella3 of 

 the masticating-lobes proceed. This appears to me to be the 

 only certain method of procedure, and^ if this be done, all the 

 secondary modifications of form &c. which take place in the 

 masticating-lobes will no longer have a disturbing effect upon 

 our conception of the morpliology of the structures. 



5. From reasons which the sequel will make readily intelli- 

 gible I propose to term the first pair of jaws in Crustacea 

 moxillvla; and the second pair maxillae. 



6. Ihe hypcpliarynx (paragnathi, lower lip, tongue) in 

 Crustacea has nothing to do with the appendages ; it is a 

 median and typically bilobed projection from the sternal 

 portion of the head behind the mouth-opening. 



II. CRUSTACEA, 

 a. ENTOMOSTEACA. 



7. On examining the integument of the sixth appendage of 

 an Ayns [Lejndnrus j^rodiicius was the particular form I 

 studied) after cleansing it with potash it is easy to see that it 

 consists of six segments, each of which is provided with a 

 lobe ; in the case of the first five the lobes are articulated to 

 their respective segments, while the sixth lobe is an immediate 

 prolongation of the corresponding segment ; the fourth and 

 fifth segnrients, at least on the posterior side of the limb, are 

 represented by distinct though small chitinous plates. On 

 the anterior side of the limb it may be distinctly seen that 

 the exopodite proceeds from the base of the third segment 

 and the epipodite from the distal end of the second (c/. § 8), 

 while the large first segment is devoid of a plate or outgrowth 

 on the outer side. In the first pair of appendages the lobes 

 of the third to the fifth segments have become very long and 

 narrow and are divided into numerous small rings. In the 

 eleventh pair of appendages in the female the external ex- 

 pansion ol the endopodite forms one half and the exopodite 

 the other half of the egg-sac j the epipodite is very small, 

 although distinct. 



