312 PROF. E. EAT LANKESTER ON THE MUSCULAR AND 



(Quart. Joum. Microsc. Sci., January 1884). Further, 1 investigated the structure of 

 both the simple and the compound (or aggregated) eyes of Limulus and of Scorpio, and 

 again obtained from the minute microscopic structure evidence of the closest agreement 

 between these two genera and of total divergence from the Crustacea (Quart. Joum. 

 Micr. Sci,, January 1883). 



Again, since the structure of the genital ducts in Crustacea is simple or, in any 

 case, non-reticulate (except in the male Apus), whilst both oviducts and sperm-ducts in 

 Scorpio and other Araclmida have the characteristic form of a mesh-work, I requested 

 my pupil Mr. W. B. S. Benham to investigate the structure of the spermatic duct and 

 glands of Limulus, hitherto unexplored. Mr. Benham found (and has described in the 

 'Transactions of the Linnean Society,' 1883) a highly subdivided reticulum, or mesh- 

 work, constituting the spermatic duct, as in the Scorpions. The oviduct had previously 

 been shown by Owen to have essentially the form of a network. 



Lastly, I have found (and am about to explain in detail in the Quart. Journ. Micr. 

 Sci. 1 ) the most intimate agreement between Limulus and Scorpio in respect of the 

 following points of minute structure :— (1) the blood-corpuscles ; (2) the softer connective 

 tissues ; (3) the entochondrite (internal sternum of Straus Durkheim), which is, in both 

 cases, a mass of condensed connective tissue with cells of very characteristic appearance, 

 but so like in the two cases as to be practically indistinguishable ; (3) the gastric caeca 

 and their lining epithelium. 



Amongst the most important points of agreement between Limulus and the Arachnids 

 is that insisted upon by Straus Durkheim, namely, the possession of an internal freely 

 suspended sternum or plastron of connective tissue (cartilaginoid tissue), to which 

 numerous muscles are attached. Such an entochondrite exists in no Crustacean 2 ; it 

 probably is more or less closely similar in nature to the so-called " chorda " discovered 

 by Leydig in insects of the genus Sphinw. 



In order to carry out fully the comparison of the entochondrite of Limulus with that 

 of Scorpio, it became necessary to make an investigation of the muscles attached to this 

 organ in each case, and this has led on to a general investigation of the whole muscular 

 system and its related supports in the two animals. The investigation of Limulus has 

 been carried out by Mr. Benham, that of Scorpio by Miss Beck. No account of the 

 muscular system of either animal has before been given, although imperfect descriptions 

 of parts of the muscular system of Limulus are to be found both in the memoirs of 

 Owen and of Alphonse Milne-Edwards. 



As might be expected, we find a considerable specialization of the muscular system 

 in the two animals compared, resulting in a wide divergence as to certain muscles ; but 

 there remain, nevertheless, certain agreements which are of the most striking and 

 important character. 



1 Since published, in January 1884. 



* I have since found a rudimentary structure of the kind in Apus (Quart. Journ. Micr. Sci., January 1884). 



