ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 979 



cxopoclites being represented by rounded tubercles. The first pair of 

 abdominal appendages are still wanting. During the fifth week the 

 young larva changes its pelagic character, loses its transparency, and 

 remains at the bottom of the water. The fifth ecdysis precedes the 

 sixth stage : the antennae are now longer than hitherto, and the asym- 

 metrical condition of the chelae is now apparent. The seventh st ige 

 ushers in the first pair of abdominal appendages, which are alike in 

 both sexes; the sexual difference being apparent only after the next 

 ecdysis, which takes place seven weeks after hatching, and the larva 

 now reaches the eighth stage, when the animal takes on its adult form. 



Monstrosities amongst Young Lobsters.* — During his study of 

 the development of the lobster, Mr. J. A. Ryder noted four types of 

 double monsters. 



The first type had no eyes ; the abdomens were separate, the 

 cephalothoraces being fused anteriorly and laterally. 



The second type had a single eye on the line of fusion of the 

 cephalothoraces. 



The third type was similarly bifid posteriorly, but there were two 

 eyes, one corresponding to the left of one lobster, the other to the 

 right one of the second. 



The fourth type had the cephalothoraces fused dorsally ; the eyes 

 and appendages were paired in each lobster. 



The fusion in these cases, where, as in the case of vertebrate 

 double monsters, the unpaired organs are fused, is due to fusion 

 coincident with gastrulation, and the gradual formation of the organs 

 of the two embryos. This principle extends the application of the 

 theory of concrescence. 



Post-embryonic Development of Telphusa.j — Signor Dott. F. 

 Mercauti gives an account of the post-embryonic development of 

 Telphusa fiuviatilis Lat. The earliest free stage was referable to the 

 Megalopa type. This form is described and further changes noted, 

 but as these consist in detailed modifications of segments and 

 appendages, they do not admit of ready summary. His results go to 

 confirm the opinion that Pscudotelphusa speciosa is an ancestral type 

 of the above form. 



Development of Oniscus murarius.J — Herr J. Nusbaum finds 

 that the endoblast is not formed at the expense of the vitelline cells, 

 but arises independently ; this is in agreement with what has been 

 found by Kowalevsky in insects and scorpions. The walls of the 

 heart arise from the mesoderm, which is not, as in insects, formed of 

 closed and distinct somites, but the mesodermal cells are scattered. 

 The term of cardioldasts is applied to those cells which form the 

 heart ; this organ grows from behind forwards. In a number of 

 points the author confirms the results of Prof. Bobretzki. 



* Amer. Natural., xx. (1886) pp. 742-3. 



t Bull. Soc. Entomol. Ital., xvii. (1885) pp. 209-1G (1 pi.). 



\ Zool. Auzeig., ix. (1886) pp. 454-8. 



3 s 2 



