ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 233 



The maxillae, labrum, and labium fuse to form a buccal tube, and the 

 chelicerse are innervated from the central ganglion ; the stomach has two 

 lateral c^ca ; there is no muscular tissue, and the oesophagus has no 

 epithelium ; there is a suctorial apparatus in the pharynx ; two tubular 

 Malpighian vessels open into the rectum and have a granular excretion 

 rich in uric acid. 



The male generative apparatus consists of two testes, two vasa deferentia. 

 and accessory glands ; the penis varies considerably in form, and offers a 

 good means for distinguishing species ; it consists of a groove, to which is 

 articulated a plate perforated by the ductus ejaculatorius ; its supporting 

 plates are movably connected with the integument, and on either side are 

 two suctorial pouches with two suckers each. The females have two 

 ovaries with long ducts, a vagina, and a receptaculum seminis, which is 

 connected with the ovaries by two short canals, and opens to the exterior 

 by a retro-anal orifice. The spermatozoa are immobile rounded cells ; the 

 gonads are developed from two cell-aggregates placed on either side of the 

 proctodaeum, and of, apparently, epiblastic origin ; the receptaculum is an 

 invagination of the hypodermal tissue which lies behind the anus. In 

 addition to the retractors of the suckers, there are others which move the 

 lower supporting plate. 



The central nervous system consists of a cerebral ganglion and a broad 

 ventral ganglionic plate ; the two are intimately connected, and there is 

 only a narrow canal between them for the passage of the oesophagus ; the 

 ganglion sends off nerves to the chelicerse and maxillary palps, and the 

 plate innervates the maxillas, feet, and abdomen ; the ganglionic cells do 

 not vary much in size ; the nerves are finely striated. 



At the first ecdysis, the fourth pair of feet are developed from the 

 imaginal discs, which underlie the third pair of the six-legged larvae ; it is 

 not correct to think that the organs of the larvae liquefy before each 

 ecdysis. Trichodadylus is sometimes ovoviviparous, and its ova are 

 attached by a stalk, the oral ovarian pole being always directed upwards. 



E. Crustacea. 



Embryology of Alpheus and other Crustacea, and the development 

 of the Compound Eye.* — Mr, H. F. Herrick studied the development in 

 Alpheus, Hijpjpia, Palsemonites, and other decapod Crustacea. 



The origin of the ovarian egg in Alpheus and in Palimirus resembles 

 that in the lobster. The fertile egg of Al^Jieus minus has a large segmenta- 

 tion nucleus, which early becomes an ill-defined mass of chromatin thread, 

 and is imbedded in a central area of protoplasm, which forms the usual 

 network inclosing the yolk-spherules. 



After two or four parts have arisen by division, the chromatin of each 

 part becomes concentrated at various points, giving rise to a swarm of 

 small nuclei, each with a distinct cell-wall and granular contents. In the 

 next stage observed, the yolks had undergone partial segmentation into 

 pyramids. 



In one species of AlpJieus this pyramidal structure is partly lost ; the 

 superficial cells are widely separated, and lie slightly below the surface, 

 and some are sunk in the yolk. They apparently form part of the 

 endoderm. In the next stage a complete blastoderm is formed and a small 

 invagination takes place ; but the cells of the endoderm are not well- 

 defined, they send processes into the yolk and at the bottom of the 



* Johns-Hopkins Univ. Circulars, vi. (1886) pp. 42-4 (1 fig.). 

 1887. R 



