Feb. 1, 1870.] 



HARDWICKE'S SCIENCE-GOSSIP. 



29 



appears to consist of a series of curved plates, over- 

 lapping one another and forming a triturating ap- 

 paratus sufficiently powerful for the soft decaying 

 substances on which the animal subsists. It cannot 

 be well made out in the living subject ; maceration 

 in caustic potash, and pressure, being necessary for 

 its exhibition. It opens into the central stomach, 

 which extends the whole length of the thorax, till 

 it terminates in the rudimentary abdomen. In the 

 species before us, it shows as a dark-greenish- 

 coloured sac, occupying the whole median line of 

 the body, with five pairs of branch stomachs or 

 cajcre proceeding from it into the two feet-jaws, and 

 eight limbs, which latter they traverse as far as the 

 last joint but three. The stomach is an important 

 organ in all creatures from man to monad, but in 

 the pycnogons it assumes a paramount importance, 

 from its performing the functions of a heart in 

 addition to its own proper sphere of usefulness. 

 Both the stomach and its prolongations are seen to 

 contract and expand at somewhat irregular intervals, 

 by which means a periodical ebb and flow of their 

 fluid contents is kept up from the stomach to the 

 caeca? and back again. The perivisceral spaces be- 

 tween the various stomachs and the walls of the 

 body and limbs are occupied by a colourless fluid 

 with corpuscles, representing the blood ; and by the 

 pulsations of the stomachs above described an im- 

 perfect system of circulation of this fluid is kept up 

 between the various cavities of the body and 

 limbs. By the expansion of the central stomach, a 

 portion of the fluid occupying the thoracic cavity is 

 propelled into one or more of the limbs, whilst by 

 the corresponding expansion of the csecse of the 

 limbs a reflex movement is produced. 



There are no branchiae or special organs of re- 

 spiration, and the oxygenation of the vital fluid 

 appears to take place through the general surface of 

 the body. The surface of the integument is studded 

 in every part with small warty excrescences, each of 

 which, on careful focussing with a l-4th objective, is 

 seen to have a central orifice. These are doubtless 

 a sort of simple spiracles, or rather breathing-pores, 

 by means of which the circulatory fluid is sufficiently 

 aerated for the support of the creature's low vitality. 

 The articulations of the body and limbs are pro- 

 vided with powerful muscles, the action of which in 

 the creature's movements can be well seen, owing to 

 the great transparency of the integument. 



Most of the foregoing remarks apply equally to 

 Achelia hispidata (fig. 36), which, however, exhibits 

 some well-marked differences in external form. It 

 is smaller and somewhat more compact than 

 Pallene, and the limbs are shorter in proportion to 

 the body. The thorax is rounder and more robust, 

 and the head (fig. 41), or, as it would I think be more 

 properly called, the proboscis, is tapered towards its 

 base and apex, giving it a less clumsy appearance 

 than the truncated cylinder of Pallene. There are 



also a pair of well-developed join ted antennae, whilst 

 the feet-jaws are very short and terminated by a 

 sort of knob instead of pincers. The large claws 

 have two smaller ones attached to their upper sides 



Fig. 39. Claw of Pallene pygmceu, x 40. 



(compare figs. 39 and 40), and the surface of the body 

 and limbs is covered with stiff bristles. In confine- 

 ment it is somewhat more active than its companion. 

 The female carries her spawn in two masses attached 

 to the false feet beneath the thorax, whilst as far as 



Fig-. 40. Claw of Achelia hispidata, x 40. 



my observations go, Pallene pygmcea carries it in a 

 single mass. I frequently observe, both in this 

 species and the last, an enlargement of the fourth 

 joints of the legs, between the caecae of which and 

 the walls of the limbs are a number of spherical 

 granular bodies resembling ova in different stages. 

 — Query : Have they any connection with the repro- 

 ductive functions ? Possibly some readers of 

 Science-Gossip maybe able to elucidate this point. 



They do not seem to be peculiar to the females, 

 as I have noticed them in specimens in which the 

 false feet are wanting, and which I therefore pre- 

 sume to be males. They certainly have very much 

 the appearance of ovaries, and I have never ob- 

 served anything resembling such organs in any other 

 part of the creature. 



The nervous system of the Pycnogonidee, accord- 

 ing to Dr. Carpenter, " consists of a single ganglion 

 in the head (formed by the coalescence of a pair), 

 and of another in the thorax (formed by the coales- 

 cence of four pairs), with which the cephalic ganglion 

 is connected in the usual mode, namely, by two 

 nervous cords, which diverge from each other to 

 embrace the oesophagus." — Microscope, p. 638. 



As regards food, the two species under considera- 

 tion must, I think, be classed under the head of 

 " scavengers." I have kept twenty or thirty in a 

 tumbler for some three months past, with a few 

 frouds of Corallina officinalis, on which are Bower- 



