November 1, 1898.] 



KNOWLEDGE 



243 



THE KARKINOKOSM, OR WORLD OF 

 CRUSTACEA.-VI. 



By the Rev. Thomas R. R. Stebbing, m.a., f.r.s., f.l.s. 



IN the preceding chapter the Cope'poda were spoken of 

 as a resourceful group. No stories of preternatural 

 ingenuity on the part of individuals can be told in 

 support of this character. Seeing that they must 

 be welcome and easily obtainable food to almost 

 every kind of aquatic animal, and that they are massacred 

 wholesale to fill the maw alike of sardine and cetacean, no 

 humane person could wish them to be very highly endowed 

 with sense and sensibility. But their individual helpless- 

 ness is pretty solidly compensated by qualities which safe- 

 guard the existence of the community. They share with 

 many other animals, higher and lower, larger and smaller 

 than themselves, a surprising fecundity. But they are not 

 content with this sort of mildly domestic defence against 

 extinction. They turn upon their devourers. They take 

 up their lodgings in the enemy's camp. They infest his 

 skin. They invade his eyes and his very mouth. They 

 enter joyfully into the spirit of Samson's riddle, " out of 

 the eater came forth meat, and out of the strong came 

 forth sweetness." They avenge the wrongs of their 

 ancestors and their cousins by sucking the blood of almost 

 every fish that swims. 



In correspondence with the extraordinary variety of their 

 dwelling-places, the parasitic and semi-parasitic Copepoda 

 present a marvellously varied array of forms, ranging from 

 those which nearly or altogether resemble the independent 

 species, through countless gr^.rlations, to the eccentric, the 



Sphi/rion lavigatum (Quoy and Graimard). M.A.S. 



abnormal, the shapeless, the unrecognizable. The recog- 

 nition of the unrecognizable may sound mysterious. The 

 key to the mystery is this, that of father, mother, and 

 children, it is usually only the mother that is absolutely 

 self-sacrificing in her indifference to any thought of personal 

 vanity when the welfare of the race is concerned. In 

 return for this it is the mother that chiefly attracts the 



attention of science by quaint peculiarities of form. The 

 mother, too, is distinguished by her respectable propor- 

 tions, being in some instances no less than thirteen times 

 as long as her diminutive husband. 



According to the Danish writers, Steenstrup and 

 Liitken, the mode in which the eggs are carried furnishes 

 a useful classificatory character. There is one series of 

 genera in which the two egg-sacks are filiform, thread-like, 

 and the eggs in each are flattened and packed one over the 

 other like a long roll of minute coins. In the other series 

 the egg-sacks are much more sack-like, the eggs are more 

 or less globular, and, though the packing is always as neat 

 as possible, it is not limited to a single line. 



Among the tree-living Copepoda, the Gymnoplea (noticed 

 in the preceding chapter) as a rule do without an egg-sack 

 or are content with only one, while the Podoplea, to which 

 the parasitic forms may be affiliated, generally have a pair 

 of these so-called sacks. The semi-parasites of the 

 family Notodelphyidse present a curious exception. There 

 is here no external ovisac, the ova being matured in a 

 pouch formed by the integument of the enlarged fourth 

 segment of the thorax. ^ Sometimes, it should be added, 

 the fifth segment of the trunk is utilized for this purpose. 

 These animals, which, as the family name implies, have the 

 matrix on the back, are found unattached and moving freely 

 about in the branchial vesicles 

 or body cavities of Ascidians. 

 for this reason one of the 

 genera has been named Ami- 

 dii-nhi. The Ascidians are an 

 accommodating set of crea- 

 tures. They take in lodgers 

 of many kinds, and especially 

 they are an important hunting 

 ground for those in search of 

 Copepoda. Even species 

 capable of living in freedom, 

 and carrying free ovisacs, are 

 not unfrequently found in 

 Ascidians. They also shelter 

 the Enteropsidfe, which are 

 not free living, but yet have 

 free ovisacs. Dr. C. Auri- 

 villius, who established the 

 family, found that in every 

 case the full-grown mother of 

 his Entfro]isis splii)i.r was, 

 along with its egg-bags, en- 

 capsuled, as it were, in folds 

 of the branchial sack of the 

 Ascidian. Thus the eggs are 

 protected by the host itself, 

 just as well as they are in 

 Xotoihlphi/s by transfer to the 

 mother's back. As Aurivillius 

 points out, this is but onemore 

 instance of Nature's inventive 

 genius applying to a single 

 purpose manifold means. 

 Enterucola cnica, Norman, 

 actually condescends to live 

 in an Ascidian's intestine, 

 which seems to be carrying condescension rather far, and 

 to be beneath the dignity of a crustacean. But odd 

 things happen in the competition for a livelihood. Other 

 species live in Mollusca. One, which abides in the 

 common cockle, is specifically known as "agile," though 



* a. S. Brady, " British Copepoda," Vol. I., p. 123. 



Ifotodelphys agilin, Thorell. 

 from Brady. 



