108 Transactions of the 



substance, which thus projects between them ; they generally about 

 equal the two parts of the zoosperms in length, and therefore 

 measure 0"012 mm. 



Kolhker * gives a figure of the zoosperms of G. rugosa, which 

 differ considerably from those of G. squammifera. The spermato- 

 phora also, according to the same author, are curious, being arranged 

 on a stalk, either branched or simple like the leaflets on a pinnate 

 leaf. 



Palemon squilla (Fig. 8) presents a type of zoosperm differing 

 from the last, and more nearly approaching that of Stenorhynchus 

 and Maia ; they consist essentially of a disk, from the centre of which 

 projects a sharp pointed rod. In those zoosperms which appear to 

 be of the normal form, one side of this disk is flat, and is bordered 

 by a substance of greater consistence than the remainder ; this 

 substance is thicker in the middle than at the sides, and from its 

 centre springs the rod, which appears to be composed of the same 

 material. The part of the disk on the side opposite the rod is 

 convex, and is composed of a soft protoplasmic material resembling 

 that which forms the knob-like portion of the zoosperms of P. 

 plaiycheles. When first examined this part looks quite smooth, 

 but it becomes very granular after remaining some time on the 

 slide: the whole disk has somewhat the shape of a saucer. On 

 obtaining a top view, the rod is seen to be implanted into the disk 

 by means of a forked base, which forms an eminence in the centre, 

 the space between the two forks being filled with a granular matter. 



The Palemon squilla has no spermatophora, but the distal 

 part of the vas deferens is filled by a very tenacious elastic sub- 

 stance, which appears to resemble in its properties that material 

 which forms the base of these bodies in P. Bernhardus and P. 

 platycheles, except that it has not become so much consolidated. 

 The vas deferens of the lobster is filled with the same kind of 

 substance. 



The forms of zoosperms in Crustacea appear to be strictly regu- 

 lated in accordance with the external shape of the animal. All 

 crabs with a square or round carapace that I have examined follow 

 the type of C. Mcvnas, and seem to vary only in the number of 

 rays. Seen on a top view, for instance, the zoosperms of Pilumnus 

 hiriellus have three rays, while those of C. Msenas, when seen 

 in that position, present so many, that it is extremely difficult to 

 determine whether they really exist or not, the usual appearance 

 being that of a circlet of granules surrounding the zoosperm, like 

 the nimbus round the head of a mediaeval saint. When we come 

 to those crabs which have a triangular carapace, like Maia or 

 Stenorhynchus, we find another type. In the Paguri, and those 

 forms which mark the transition between the Brachyura and the 



* 'Ann. Sciences Natiirelles,' 2™^ Se'rie, tome 19, 1843. 



