462 ' PROF, OWEN ON THE ANATOMY 
The body of the American as of the Moluccan King-crab (Limulus) consists of three 
principal parts—two large, broad, depressed, and shield-shaped, as viewed from above 
(Pl. XXXIX. A., B), the third long and spike-shaped (ib. c). 
` For the description of the external characters of these parts, which are not here 
noticed, I refer to the elementary works on Crustacea and to the undercited excellent 
treatise by Van der Hoeven*. 
The homologies propounded by the Dutch monographer have not, however, been 
generally accepted. “It is evident," he remarks, “that the foremost division [* premier 
bouclier'] answers to the head and thorax of insects; for the feet are attached thereto, 
whilst it bears on its upper surface the organs of vision. Thus the head is here con- 
founded with the thorax, and we believe ourselves authorized to give to this first buckler 
the name of * Cephalothorax, which naturalists assign to the first part of the body of 
Arachnidans” +. 
This homology seems not to have been so evident to subsequent crustaceologists. 
Milne-Edwards, Thos. Bell, Spence Bate, Prof. Dana, and, above all, those eminent 
observers, Salter, Huxley, Woodward, who have devoted themselves so laboriously and 
successfully to the study of the palseozoic Crustacea, to which Limulus is most closely 
allied, reject it. According to them, the ‘cephalothorax,’ V. der H., answers only to 
the “head” of Insects and Crustaceans. 
There is, of course, a corresponding discrepancy as to the homology: of the second 
division of the body of Limulus. “Le second bouclier répond à l'abdomen des Arach- 
nides," according to V. der Hoeven. It is the ‘thorax’ of the above-cited later 
earcinologists. 
At this point I venture to submit the following remarks :—The first division (A in all 
the plates), which constitutes, in Limulus, the major part of the entire body, which 
includes, besides the mouth, the brain, and organs of sense, also the major part of the 
neural axis, the same proportion of the heart and of the genital organs, together with the 
stomach, liver, and half of the intestinal canal, has obvious analogies with both head and 
abdomen of higher animals. The second division (B in all the plates), which in both 
Limulus and Scorpio includes the lamellate respiratory organs, the continuation of the 
heart, of the intestine, and of the neural axis, with the terminal outlets of the genital 
organs, as obviously repeats characters of both thorax and abdomen of higher animals. 
The so-termed ‘cephalothorax’ of Arachnology, which is, as Van der Hoeven rightly 
recognized, the homologue of the first division of the body of Limulus, does not include 
the segments and appendages answering to those called ‘thoracic’ in modern crustace- 
ology. The “abdomen” of Scorpio (Audouin) and of Limulus (Van der Hoeven) does 
correspond with the so-called * thorax ' of carcinologists. | 
To apply the terms *cephalon,' ‘ caput,’ or ‘head, to the division of the body of Li- 
mulus, above characterized, seems, howeyer, to be an extension of the use of suth term 
beyond fair and reasonable bounds. 
* Van der Hoeven, ‘ Recherches sur l'Histoire Naturelle et Y Anatomie des Limules, fol. 1838. The species which 
he dissected was the rapier-tailed Molucca Crab (Limulus rotundicauda, Latr.). 
+ Ib. p. 10. t Op. cit. p. 11. 
