133 



have been divided by Viallanes 5 into three divisions; i. e. the proto- 

 cerebrum, deutocerebrum , and tritocerebrum ; these have divisions 

 corresponding to the supposed three preoral segments of the head. At 

 present I do not think that there are more than two preoral segments, in 

 the head of insects. SaintRemy shows that the brain of the Myrio- 

 pods has the same divisions , and is homologous Avith that of insects 

 and Crustacea. He shows, however, that the brain of Arachnids lacks 

 the deutocerebrum, while the tritocerebrum of Insects, Crustacea, and 

 Myriopoda is represented by the rostro-mandibular ganglion of the 

 Arachnida. 



As the brain of Limnlus does not, contrary to that of Spiders and 

 Scorpions, send nerves to the first pair of appendages, and has only at 

 the most three pairs of lobes, and originally, according to Patten, three 

 pairs of neuromeres , representing a first and second median-eye, and 

 a third, or lateral-eye segment, it follows that no deutocerebrum or 

 tritocerebrum is represented in its brain. 



It seems to us that this lack of homology between the brain of Limu- 

 lus. and that of Arachnids added to the other brain-characters we have 

 pointed out, together with the different mode of grouping of the appen- 

 dages, and their shape; also the absence of urinary tubes, of tracheae, 

 and the presence of branchiae , forbid the association of Limulus and 

 other Podostomata (Merostomata and Trilobita) with the Arachnida, 

 but are so fundamental as to warrant their forming a class by themsel- 

 ves. On the other hand both embryology and morphology show that 

 the Arachnida and Podostomata probably had a common origin, one 

 group becoming adapted to the land, the other and older, having origi- 

 nated in the sea. The Insects and Myriopoda may have had a common 

 origin, while the Crustacea probably had an independent origin. 



Providence, R. L, U. S. A., Brown University, Febr. 25. 1891. 



4. The Deveiopment of the American Lobster. 



By F. H. H er rick, Ph. I), of Adelbert College, Cleveland, Ohio, U. S. A. 



eingeg. 21. März 1891. 



This paper is an abstract of researches conducted during the part 

 of two summers (1889— 1890), at the laboratory of the U. S. Fish Com- 

 mission at Woods Holl, Massachusetts. It deals mainly with the early 

 stages in the development of the eggK The general statements which 

 follow in regard to the habits of the American lobster [Homarus ameri- 



& Annales des Sc. Nat. VIL Ser. Tom. IV. 108. 1887. 



i For a fuller preliminary statement, see the Johns Hopkins University Circu- 

 lars, No. 80. 



