83 



quitting the ovary is surrounded by a true chorion. Sars 

 and Dohrn have described a second membrane as existing 

 when the egg is laid ; but this is really, according to Dr. 

 Van Beneden, an embryonic structure — " the blastodermic 

 cuticle."' In Asellus the first phases of yelk cleavage 

 are wanting, the cleavage being merely superficial, and the 

 formation of the blastodermic cells results from the multipli- 

 cation of the original egg- cell, a gradual separation between 

 the protoplasmic and deutoplasmic elements of the yelk 

 taking place. The blastoderm is not formed, as Dr. Dohrn 

 believed, at the expense of a blastema in which the cell- 

 nuclei develop by free formation. The enigmatical em- 

 bryonic organs known as " Blattforraige Anhange,"' " micro- 

 pyle apparatus,"' " trefoil-like appendages," which Dr. Van 

 Beneden terms " appendices foliaces," arise from the posterior 

 part of the cephalic lobes in the course of embryonic growth. 

 They burst through the blastodermic cuticle and the chorion 

 in the course of their development. As soon as these tran- 

 sient appendages have attained their full growth the perma- 

 nent appendages commence to make their appearance, and 

 Dr. Van Beneden maintains that the first and second pair 

 of antennte are the first to appear, contrary to Dr. Dohrn's 

 statement. ' In this state the embryo represents the well- 

 known four-armed Nauplius form of crustacean development. 

 A cuticle now forms on the surface of the embryo, which is 

 the larvenhaut or nauplian cuticle, and is shed after the blasto- 

 dermic cuticle has been moulted. The chorion, blastodermic 

 cuticle, and nauplian cuticle having been successively shed, 

 the embryo comes forth from the maternal pouch in its adult 

 form. 



No. 3 treats of the aberrant Decapod Mysis ferruginea. In 

 this case, also, there is a partial yelk cleavage, resulting in a 

 complete envelopment of the eg^ by the blastoderm. The 

 existence of a primordial cellular ridge is pointed out, which 

 is exactly homologous with the cellular column (Keimhugel) 

 of Hemiptera, Orthoptera, and Lepidoptera. By the study 

 of the changes of this part the homologies of the parts and 

 appendages of the cephalic lobes, &c., in these two groups 

 of Arthropods may be fixed with certainty. The mandibles 

 and antenuse give their first indications at the same time, 

 and after the caudal lobe, which is bent back under the 

 ventral region, as in all Decapods. The nauplian cuticle 

 is the first which Mysis develops. There is no blastodermic 

 moult. The trefoil appendages of Asellus, Peneus, &c., are 

 represented on the flanks of the embryo Mysis. 



No. 4 relates to the eggs of the crustaceans of the genus 



