Dr. F. Miiller on the Transformations of the Porcellanse. 49 



The parts of the mouth (fig. 5) consist of a very large upper 

 lip (c), of two strong sharply toothed mandibles, apparently 

 without palpi {d), of a bipartite lower lip [e), and two pairs of 

 maxillae [fg]- The anterior maxilla (fig. 8) is split up into three, 

 and the posterior one (fig. 9) into five leaves armed with strong 

 bristles, which are partially denticulated or feathered ; the latter 

 also bears on the outside a larger membranous plate, which is 

 produced posteriorly into a finger-like process ; the process bears 

 one, and the plate itself anteriorly and at the margin six, plu- 

 mose bristles. This plate is bent upwards, and is in constant 

 motion between the body and the carapace. 



The two pairs of natatoiy feet consist of a strong cylindrical 

 basal joint and two terminal rami ; the inner ramus, which the 

 animal is fond of extending forward, has four joints, and the 

 outer one, which is usually turned outwards and upwards, two, 

 less distinctly separated. At the extremity of the outer ramus 

 stand four long plumose setae ; a single plumose seta is at the 

 end of the third joint of the inner ramus of the last pair, and 

 there are simple bristles on all the joints of the inner ramus of 

 both pairs. 



Behind the origin of the natatoiy feet commences the six- 

 jointed abdomen, which bears no appendages; this separates 

 from the carapace a little behind the middle of its upper part. 



The stomach is somewhat dilated, and already exhibits (at 

 least in Porcellina) longitudinal ridges beset with bristles ; close 

 to it on each side there are two hepatic caeca directed forwards, 

 and two others directed backwards ; the intestine has a straight 

 course, and opens a little before the middle of the caudal seg- 

 ment. 



The heart, situated at the posterior end of the thorax (in 

 young Crabs under the origin of the dorsal spine), appears to be 

 already formed exactly as in the mature animal, and to give off" 

 the same vessels. The anterior single vessel may be readily 

 traced almost to the apex of the frontal horn, to the upper wall 

 of which it is applied. Blood-corpuscles are exceedingly few^ in 

 the first days (but this does not apply to all Zoea). 



In each abdominal segment there is a ganglion of consider- 

 able size, united to its neighbours by two separate cords ; in the 

 anterior part of the animal I could not quite cleai'ly make out 

 the nervous system in its connexions. 



If it be easy to procure in abundance the earliest stages of 

 the most various Crustacea, it is all the more difficult to obtain 

 a clue to their ultimate fate. Although the Porcellance are 

 among the most generally distributed of Crustacea, I only once 

 (in December of last year) met with an older larva (Pl.I.figs.6,7). 

 At the spot where I found it, neither Porcellina stellicola nor 



Ann. ^ Mag. N. Hist. Ser. 3. Vol xi. 4 



