222 SUMMARY OF CURRENT RESEARCHES RELATING TO 



which first branches off, and with that of the Enteroi>neusta which is 

 intermediate in jjosition. U'he Tracheata and Crustacea are regarded 

 as independent phyla, Limiilus being phiced with the former. The 

 autlior is careful to recognize degradation as well as ascent. His 

 work will be very uscsful to those for whom it is intended, and " along 

 with a good text-book or as a supplement to a course of lectures on 

 zoology." 



B. INVERTEBRATA. 



Chitin as a Constituent of the Cartilages of Limulus and Sepia.* 

 — W. D. Halliburton has submitted to chemical analysis the cartilages 

 occurring in the head of Sepia and the eutosternite of Limulus. 



The basis of the cartilage is a chondrin-like body, which gives 

 the reactions of mucin and gelatin. But the gelatinous element is 

 exceedingly small, and no gelatinization occurs on the cooling of the 

 hot water extract. The cartilage differs, however, from that of Ver- 

 tebrates in containing a small percentage of chitin ; in the case of 

 the entosteruite of Limulus I'Ol per cent, and of Sepia 1 22 percent. 

 He has also demonstrated that chitin exists in the liver of Limulus, 

 though whether in the connective tissue or in the liver-cells them- 

 selves is undetermined. The method of analysis is fully described. 



These results are especially interesting as showing that chitin is 

 not confined to the epiblast, for in three instances it has been shown 

 to occur in mesoblastic structures. 



Mollusca. 



Eye of Gastropoda.f — C. Hilger, finding that his predecessors 

 in the investigation of the eyes of Gastroi:)ods, have examined a few 

 species only, has studied those of a considerable number of species. 

 He points out that two kinds of optic organs have come under his 

 consideration. 



In the first the eye remains in a somewhat embryonic condition, 

 and forms but a slight invagination of the epithelium of the body ; 

 such are found in the lowest Prosobranchiata, the Cyclobranchiata and 

 the Aspidobranchiata ; Margarita, Fissurella, Haliotis, Patella, and 

 Troclius may be cited as examples. In the second series the eye 

 forms a completely closed capsule, which is invested by connective 

 tissue ; it is seen in Conus, Cyprcea, Fusus, Nassa, Murex, and others. 



In the simpler type the eye has the form of a cup- or bell-shaped 

 invagination of the epithelium of the body ; in most cases the cuticle 

 seems to form an extremely thin lamella over the- anterior part of the 

 vitreous body ; the invagination is lined by the retina which, anteriorly, 

 passes directly into the epithelium of the body, and is invested 

 externally by the outspread optic nerve. In Haliotis and Trochus 

 the cavity is filled by a delicate gelatinous substance, and in Patella 

 and Nacella by a finely granulated mass. 



In the more advanced type, the larger and hinder part of the cor- 



* Quart. Joum. Micr. Sci., xxv. (1885) pp. 173-81. 

 t Morphol. Jahrb., x. (1884) pp. 3r)l-71 (2 pis.). 



