April, 1902.] 



KNOWLEDGE 



characteristic of the whole <»roiip. There is also a 

 Pallene emanaln, the starveling Palleiie. Some may Ije 

 incline*] t« sutj.tj<'s' *'"*' '* ''^'^^ ''"' ^'"•'■'y teniiity of the 

 almost evapijr.itins,' trunk tiiat put a force upon nature to 

 make a grotesque use of the jointed legs. Nothing of the 

 kind can be truly urged. In the Ca]>rillidea, where also 

 such names as sixH'tre-shrimp and skeleton- shrimp are 

 applicable and have actually been applied, and in equally 

 thread-like amphipods of the genus Khahdnsomn, no such 

 deyice is made use of. Nature there arranges that the 

 intestinal and ovarial apparatus shall In- in their ordinary 

 situation, and, as though to prove an unfettered iude- 

 jiendence of action, goes about in those very instances to 

 diminish the num'^er or the size of the jointed limbs. 



Pallene breviroslrU, Johnston. After Sars. 



From the figure of Pallene it will be seen that the eggs 

 are formed in the dilated fourth joint of the walking-leg. 

 This is their usual ]>osition, and they occur not in one leg 

 onlv but in each of the eight. The sexual ojjeuings of 

 both male and female are in the second joint. Asa rule 

 those of the female are found in the second joint of all the 

 eight legs, those of the male only in the last two pairs, 

 though sometimes in the last three or limited to the last 

 jKiir of all. The genus Pycnogoiium has them for both 

 sexes only in the last pair of legs. Though so strangely 

 ramified and well provided with orifices the ovary is found 

 to be, strictly speaking, a single structure. This, however, 

 is subject to the presumption from analogy that at a 

 particular point of the body two members of an original 

 pair have coalesced. The ovarial prolongations usually 

 extend only to th • end of the fourth joint of the leg, but 

 Dr. Dohrn describes a species, found commonly in the Bay 

 of Naples, and named by him Clotenia conirostris, in which 

 the ovaries extend to the end of the sixth joint in all the 

 legs, •' producing along the whole stretch ripe eggs which 

 are of considerable size and give the legs a striking 

 appearance." 



The numljer of eggs that are laid, or at least that the 

 male has to take charge of at any one time, is very variable. 

 In the genus Pallene, Professor Sars and Dr. Dohrn call 

 attention to the fewness of the eggs. In the British 

 species P. breviroatrie, Sars says that they are as a rule 

 about six on each leg, and he speaks of them as similarly 

 few in number in P. produrta. a species which he describes 

 from Norway. A specimen, however, taken off Millport 

 iu the Clyde, having characters which seem to justify its 

 identification with P. prodiictn, carries thirty-eight eggs in 

 one packet and forty-six in the other. This species does 

 not appear to have been previously recorded from Great 

 Biitain. 



An Irishman explained the want of hospitality from 

 which he had suffered by saying that no one had thought 



of asking him, Have you a mouth, Patrick ? In the 

 Pycnogonida there is indeed a mouth, though to match 

 the rest of the structure a peculiar one, of which the 

 descriiition must bo deferreil to a later opportunity. It is 

 mentioned here as undoubtedly the orifice through which 

 food is introduced, and because it leads as iisual into the 

 intestine of which some other characters are so very un- 

 usual. It might be thought singularity enough for an 

 alimentary canal to push prolongations through numerous 

 joints of the strongly geniculating limbs and sometimes 

 also into the proboscis of its owner. But this is not 

 suflBciently exceptional by itself to satisfy the Pycnogonida. 

 With crustaceans the Intestinal tube, whether it be straight 

 or curly, is very commonly made conspicuous to the 

 observer and defined throughout its course by its dark 

 and compact contents. There is a column of residual 

 matter from the food which has served its purpose of 

 alimentation. There are arrangements for the expul- 

 sion of these waste products from the body. But 

 iu the Pycnogonida no such residuum is perceived, 

 even when their bodies are so translucent as to show 

 clearlv the ganglia and commissures of the nerve-chain. 

 No naturalist appears to have witnessed in these 

 animals that expulsion of reliquioe, of which most 

 arthropods and vertebrates are at little pains to make 

 any concealment. There are, however, the requisite 

 muscles for opening and closing the aperture of the caudal 

 segment, and of this Dr. Meinert remarks that " the 

 intestinal canal opens in the end of it with a weak 

 squirting apparatus." But Meinert's observations were 

 made on presei-ved specimens, whereas Dr. Dohrn says : 

 "In spite of hundreds of observations of living Pycnogonida 

 under the microscope I have never seen the exit of solid 

 material from the terminal orifice, nor ever remarked 

 coloured fluids iu the end part of the intestine." He is 

 driven, therefore, to sujipose that these creatures can 

 avoid importing into their organism anything indigestible, 

 or that they can iu some way absorb all that they actually 

 swallow. It seems a truly ethereal system of eating and 

 drinking. Dohrn thinks that it may help to explain 

 another difficult point. The Pycnogonida have no traclieoe, 

 no lung-books, no branchiae, and in Dohrn's opinion the 

 iutegument is not permeable for that interchange of gases 

 which is necessary to respiration. Yet they must breathe, 

 and as the terminal aperture has been redeemed from 

 vulgar uses and left with nothing to do, he lets them 



Barana castelli, Dohrn. Only appendages of right side shown. 

 After Dolirn. 



breathe through that. Hoek inclines to think this solution 

 of the problem rather rhapsodical, or as one might say 

 Aristophanic* He prefers to believe that the skin is in 



♦ See Aristophanes, The Clouds, line 159, but compare also Huxley, 

 The Cravfish, note viii. , p. 353. 



