INTRODUCTION. xliii 



generally fringed with hairs. One of these plates is 

 developed on the inner side of each of the two pairs of 

 gnathopoda (Fig. 17), and the two 

 an terior pairs of pereiopoda. These 

 plates overlie each other in a compact 

 form, securely protecting the ova, or 

 the immature young, from external 

 accidents, as shown in fig. 10, p. xxxiii. 

 It is the opinion of Von Siebold 

 that these appendages are periodically 

 developed at the " epoque du rut." 

 FIG. 17. This we have not, from our own obser- 



vation, been able to verify, having taken females during 

 all periods of the year with these appendages fully de- 

 veloped. They are absent on the young females. We 

 believe, however, that, when they are once developed, 

 they continue permanent organs, only disappearing as the 

 result of accident. 



In the Anceida, the incubatory pouch appears to belong 

 to the three posterior segments of the pereion. By the 

 continued growth of the ova, the pereion is reduced to a 

 most impoverished state. The alimentary canal being in 

 a collapsed condition, and always empty, the animal can 

 only be viewed in the light of a great egg-producer, after 

 the' development of which an empty sac only is left, the 

 poor remains of a worn-out animal. 



The^ history of the development of the ovum from 

 its impregnation to the development of the perfect larva 

 has been best worked out by Valette St. George in 

 the Amphipoda, and Anton Dohrn in the Isopoda. We 

 must refer the student to the memoirs of these two 

 authors for a detailed account of the germination and 

 growth of the ovum in all its stages. It will suffice for 

 us to say, that it appears to be clearly established by 



