. CRUSTACEA. 185 



as well as the structure of this part. Certain appendages of 

 the first and second abdominal rings in the male crabs ai-e probably 

 connected as exciting organs with the sexual function. 



The female organs present, like the male, a progressive compli- 

 cation of structure as the species ascend in the class. Most of the 

 small Entomostraca carry the impregnated ova in appended ovisacs, 

 like those of the Lerneee. These sacs are not developed in the Lim- 

 ulus, which also, differs from the smaller Entomostraca, inasmuch as 

 the ovarian mass interblends its lobes and processes with those of the 

 liver ; the oviducts form more frequent communications with each 

 other than in the higher Crustacea, but ultimately terminate, like the 

 vasa deferentia, by two distinct but continuous orifices on the back 

 part of the first abdominal lamelliform appendage. 



The ovaria in the lobster are of great length on each side ; the 

 oviduct comes oft' from the outer part of nearly the middle of the 

 gland, and descends to terminate at the basal joint of the third pair 

 of ambulatory feet.* 



In the Brachyura the female apparatus reaches its highest state of 

 complication, and consists of an ovary, oviduct, and a copulatory 

 pouch, or spermatheca, on each side. The ovaria are elongated 

 cylindrical sacs in the Maia, and are divided into an anterior and a 

 posterior part, the short oviduct being continued from the union of 

 the two : the anterior parts of the ovaria are united together by a 

 short transverse canal ; the posterior divisions are very intimately 

 united through half their extent : the spermatheca is developed a. 

 little above the termination of each oviduct. 



The species of a genus of Macroura {Mijsis) are called " Opossum 

 shrimps," from carrying their ova during the process of development 

 in abdominal recesses, analogous to the marsupial pouch ; but tliis 

 superadded complexity in the reproductive economy is common, 

 under various modifications, to all the Crustacea. 



The ova, after extrusion from the oviducts, are retained and pro- 

 tected in the Cymothoa and other sessile-eyed Malacostraca under 

 their thorax by means of the flabelliform appendages of the ex- 

 tremities, which appendages are unusually expanded, and overlap 

 each other, so as to form a marsupial cavity or temporary receptacle, 

 in which the incubation of the ova is completed. In the Podoph- 

 thalma, the lamelliform ciliated appendages of the abdominal seg- 

 ments include similar marsupial or incubatory recesses for the ova. 

 The female lobster and other Macroura are distinguished from the 

 male by the greater development of these appendages; and in the 



* Prep No. :5188. 



