42 PEOF. M. M. HAETOG ON THE 



the many-chambered heart of the proper Phyllopods as primitive, there seem to me 

 equally strong ones for believing it to be rather a new development, connected with 

 the strong segmentation of the long body, like what we find in the very aberrant 

 Stomatopods, a group in which the similar heart cannot but be regarded as merely 

 homoplastic with that of Phyllopods, if the Leptostraca {Nebalia) be the parent form of 

 the Stomatopods. In Nebalia there are the above three large, well-marked venous ostia, 

 but besides these there are smaller ones — one pair in front of the large lateral pair, and four 

 " ganz klein " pairs, nearly dorsal, between these anterior and the posterior pairs ; another 

 lateral pair is added at the last moult, between the anterior lateral pair and the foremost 

 of the dorsal ones. Now this shows that in Nebalia an increase in the number of ostia 

 takes place just at the last moult, and the curious positions and varying size of the ostia 

 squares with the possibility of this heart being derived from the simple heart of the 

 Copepod and Zosea, independent of the segmented heart of the Eranchiopod. With the 

 strong development and concentration of the cepbalothorax which I ascribe to the 

 primitive Crustacean, its heart must have been a short one, and many Zosese show the 

 same condition of the heart as we find in Copepoda. Moreover, if we compare Crustacea 

 with Chsetopoda, we find many a reason for believing the heart of the former to be a new 

 structure, possibly derived from intersegmental septa or mesenteries. In that case it 

 could only have been formed in the roomy cepbalothorax, and would have had the 

 Copepod form. 



The circulation is effected in some of the Parasitic Copepoda, according to Claus, 

 Pickering, and Dana *, by contractile mesenteric valves ; and in all of that group, which 

 I regard as off tilie main line of Crustacean descent, the blood-corpuscles are said to be 

 floating rather than wandering cells. 



I may here note that there seems very little reason for connecting the so-called blood- 

 system of Arthropods — at least of Crustacea — with the proper blood-system (pseudhsemal) 

 of Annelids ; the former always containing the amoeboid coelomic corpuscles, the latter 

 special corpuscles derived from its walls, and, indeed, in this respect corresponding, as 

 in so many others, in a measure with the blood-system of the Vertebrate embryo. 



{g). The General Form of the Body. — If we try and figure to ourselves an ideal Crus- 

 tacean, that shall combine the characters of as many groups as possible, including, too, 

 such larval forms as Zoaea, we find that we have an Arthropod with a strong and large 

 cepbalothorax, its segments fused anteriorly, and with bifid limbs on its ventral surface, the 

 cepbalothorax appendages used for progression and apprehension of food, and the abdomen 

 reduced to a jointed tail with ill-developed appendages, and made by the enlargement of 

 the dorsal end into an efficient caudal rudder or fin. Of svich a type are all Protozoseaj, 

 and most Zoa?ae, Nebalia, Cuma, and many adult Macrura ; and it occurs, disguised by 

 the shell, in many Cladocera and Ostracoda. This is the characteristic form of Copepoda 

 generally, which, indeed, corresponds absolutely with the Erichthya larva of Stomatopods, 

 save for the better-developed pleuraj of the latter, and its widely expanded telson. If we 

 imagine how the creeping Chsetopod evolved into tlie Crustacean, we shall see that 



* Sco (jerstiiuker in Bronu s Thiur-lleich, lid. v. p. G.jG. 



