94 Descriptions of Pf'eparations. 



its exact homologues, inasmuch as they correspond in strictness 

 with the two terminal joints of its mandibular palp. The four 

 posterior of the five abdominal legs of either side consist each 

 of seven joints, seven being considered by Mr. Spence Bate to 

 be the typical number of the joints in the normally developed 

 appendage of every kind in Crustaceans. The second and third 

 joints are anchylosed in the anterior of these five appendages^ as 

 they are in all the five of the Brachyura, so as to reduce the 

 number of separate joints to six. The proximal joint is known 

 as the ' coxopodite / a black bristle is in this (female) specimen 

 introduced into the oviduct, which opens in Macrurous and Ano- 

 murous Decapods, as also in Hedriophthalmata, in the coxopodite 

 of the third abdominal appendage. The second joint is known 

 as the 'basipodite/ or 'basis.^ It is in the interval between the 

 'basi-'' and 'coxopodite^ that the separation of the limb takes place 

 when a Crustacean throws it ofi" in consequence of fright or injury. 

 The third, or ' ischiopodite/ is marked by an annular constriction a 

 little way distally to its articulation with, when it is distinct from, 

 the basipodite. This constriction may perhaps represent the aborted 

 exopodite, which in the three posterior abdominal legs of Squilla 

 is articulated to the third segment of the appendage ; by observing 

 its presence we are enabled to identify the various segments in the 

 appendages of the abdomen in Brachyura. The fourth, the longest 

 of all the segments in all the five appendages except the first, is 

 known as the 'meropodite,' and has been compared with the 'femur ^ 

 of insects ; the fifth is known as the ' carpopodite,' and the two 

 terminal are known as ' propodite' and ' dactylopodite,^ and have 

 been compared to the ' tibia^ and ' tarsus^ of insects. The append- 

 ages on the first post-abdominal segment are rudimentary; to 

 the hairs upon the appendages of the succeeding segments, some 

 of the large ova of this fresh-water Decapod may be observed to 

 be attached. The appendages of the second, third, fourth and 

 fifth post- abdominal segments consist of a biarticulate ' protopo- 

 dite,^ the proximal segment of which is smaU and annular, and 

 the distal cylindriform ; and of two multiarticulate filaments repre- 

 senting an ' exopodite ' and an ' endopodite,^ the basal segment 

 of the latter of which is much the largest in either series. The 

 appendages of the sixth abdominal segment form the powerful 

 'swimmeret^ of the crayfish. The lateral elements of this organ 



